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NOAAFSYB-A 72-1
,*^'''°"^o^
Fishery Bull
National Oceanic and Atmospheric Administration • National Mar
Vol. 72, No. 1 January 1974
KITTREDGE, J. S., FRANCIS T. TAKAHASHI, JAMES LINDSEY. and REUBEN
LASKER. Chemical signals in the sea: Marine allelochemics and evolution 1
FULLENBAUM, RICHARD F., and FREDERICK W. BELL. A simple bioeconomic
fisheiT management model: A case study of the American lobster fishery 13
OLLA, BORI L., ALLEN J. BEJDA, and A. DALE MARTIN. Daily activity, move- ments, feeding, and seasonal occurrence in the tautog, Tautoga onitis 27
LENARZ, W. H., W. W. FOX, JR., G. T. SAKAGAWA, and B. J. ROTHSCHILD. An examination of the yield per recmit basis for a minimum size regulation for Atlantic yellowfin tuna. Thniiiius albacares 37
FLEMINGER, A., and K. HULSEMANN. Systematics and distribution of the four
sibling species comprising the genus Pontellina Dana (Copepoda. Calanoida) 63
HUGHES, STEVEN E. Stock composition, growth, mortality, and availability of
Pacific saury, Cololabis saira, of the northeastern Pacific Ocean 121
ANAS, RAYMOND E. Hea\y metals in the northern fur seal, Callorhiinis ursinus,
and harbor seal, Phoca vituUita ricliardi 133
WAHLE, ROY J., ROBERT R. VREELAND, and ROBERT H. LANDER. Bio- economic contribution of Columbia River hatchery coho salmon. 1965 and 1966 broods, to the Pacific salmon fisheries 139
POWELL, GUY C, KENNETH E. JAMES, and CHARLES L. HURD. Ability of male king crab. Paralithodes camtschatica, to mate repeatedly, Kodiak, Alaska, 1973. 171
WICKHAM, DONALD A., and GARY M. RUSSELL. An evaluation of mid-water
artificial structures for attracting coastal pelagic fishes 181
GRANT, GEORGE C. The age composition of striped bass catches in Virginia
Rivers, 1967-1971, and a description of the fishery 193
PEARCY, WILLIAM G., and SHARON S. MYERS. Larval fishes of Yaquina Bay.
Oregon: A nurser>' ground for marine fishes? . 201
PARK, TAISOO. Calanoid copepods of the genus Aetideus from the Gulf of Mexico . . 215
LIGHTNER. DONALD V. Normal postmortem changes in the brown shrimp, Pe)iaeus
aztecHH 223
STRUHSAKER, PAUL, and ROBERT M. MONCRIEF. Bothii^ thonip.s(>,ii (Fowler)
1923. a valid species of flatfish (Pisces; Bothidae) from the Hawaiian Islands 237
Note
CABLE, WAYNE D., and WARREN S. LANDERS. Development of eggs and em-
biyos of the surf clam, Spisula Holidissinia, in synthetic seawater 247
Seattle, Wash.
U.S. DEPARTMENTOFCOMMERCE
Frederick B. Dent, Secretary
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
Robert M. White, Adminisfrator
NATIONALMARINE FISHERIES SERVICE Robert W. Schoning, Director
Fishery Bulletin
The Fishery Bulleiin carries original research reports and technical notes on investigations in fishery science, engineering, and economics. The Bulletin of the United States Fish Commission was begun in 1881; it became the Bulletin of the Bureau of Fisheries in 1904 and the Fishery Bulletin of the Fish and Wildlife Service in 1941. Separates were issued as documents through volume 46; the last document was No. 1103. Beginning with volume 47 in 1931 and continuing through volume 62 in 1963, each separate appeared as a numbered bulletin. A new system began in 1963 with -volume 63 in which papers are bound together in a single issue of the bulletin instead of being issued individually, Beginning with volume 70, number 1, January 1972, the Fishery Bulletin became a periodical, issued quarterly. In this form, it is available by subscription from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. It is also available free in limited numbers to libraries, research institutions. State and Federal agencies, and in exchange for other scientific publications.
EDITOR
Dr. Reuben Lasker
Scientific Editor, Fishery Bulletin
National Marine Fisheries Service
Southwest Fisheries Center , La Jolla, California 92037
Editorial Committee
Dr. Elbert H. Ahlstrom
National Marine Fisheries Service
Dr. William H. Bayliff
Inter-American Tropical Tuna Commission
Dr. Daniel M. Cohen
National Marine Fisheries Service
Dr. Howard M. Feder University of Alaska
Mr. John E. Fitch
California Department of Fish and Game
Dr. Marvin D. Grosslein National Marine Fisheries Service
Dr. J. Frank Hebard
National Marine Fisheries Service
Dr. John R. Hunter
National Marine Fisheries Service
Dr. Arthur S. Merrill
National Marine Fisheries Service
Dr. Virgil J. Norton University of Rhode Island
Mr. Alonzo T. Pruter
National Marine Fisheries Service
Dr. Theodore R. Rice
National Marine Fisheries Service
Dr. Brian J. Rothschild
National Marine Fisheries Service
Mr. Maurice E. Stansby National Marine Fisheries Service
Dr. Maynard A. Steinberg National Marine Fisheries Service
Dr. Roland L. Wigley
National Marine Fisheries Service
Kiyoshi G. Fukano, Managing Editor
The Secretary of Commerce has determined that the publication of this periodical is necessary in the transaction of the public business required by law of this Department. Use of funds for printing of this periodical has been approved by the Director of the Office of Management and Budget through May 31, 1974.
Fishery Bx^^
LIBRARY CONTEN'l^y 2 0 1974
Vol. 72, No. 1 I Woods Hole, M^'^ j^^^^^.^ ^^._^
KITTREDGE, J. S., FRANCIS T. TAKAHASHI, JAMES LINDSEY, and REUBEN
LASKER. Chemical signals in the sea: Marine allelochemics and evolution 1
FULLENBAUM, RICHARD F.. and FREDERICK W. BELL. A simple bioeconomic
fishery management model: A case study of the American lobster fishery 13
OLLA, BORI L., ALLEN J. BEJDA, and A. DALE MARTIN. Daily activity, move- ments, feeding, and seasonal occurrence in the tautog, Tautoga ojiitis 27
LENARZ, W. H., W. W. FOX, JR., G. T. SAKAGAWA. and B. J. ROTHSCHILD.
An examination of the yield per recruit basis for a minimum size regulation for Atlantic yellowfin tuna. Tliuinuis albacares 37
FLEMINGER, A., and K. HULSEMANN. Systematics and distribution of the four
sibling species comprising the genus Pontellina Dana (Copepoda. Calanoida) 63
HUGHES, STEVEN E. Stock composition, growth, mortality, and availability of
Pacific saury, Cololabis saira, of the northeastern Pacific Ocean 121
ANAS, RAYMOND E. Heavy metals in the northern fur seal, CaU(i)-hi)tus ursi)iHs,
and harbor seal, Pltoca rituliiia richardi 133
WAHLE, ROY J., ROBERT R. VREELAND, and ROBERT H. LANDER. Bio- economic contribution of Columbia River hatchery coho salmon, 1965 and 1966 broods, to the Pacific salmon fisheries 139
POWELL, GUY C, KENNETH E. JAMES, and CHARLES L. HURD. Ability of
male king crab, Paralithudes ca nitschatica , to mate repeatedly, Kodiak, Alaska, 1973. 171
WICKHAM, DONALD A., and GARY M. RUSSELL. An evaluation of mid-water
artificial structures for attracting coastal pelagic fishes 181
GRANT, GEORGE C. The age composition of striped bass catches in Virginia
Rivers, 1967-1971. and a description of the fishery 193
PEARCY, WILLIAM G., and SHARON S. MYERS. Larval fishes of Yaquina Bay,
Oregon: A nursery ground for marine fishes? 201
PARK, TAISOO. Calanoid copepods of the genus Aetideus from the Gulf of Mexico . . 215
LIGHTNER, DONALD V. Normal postmortem changes in the brown shrimp, Peiiaei(s
aztt'cn!< 223
STRUHSAKER, PAUL, and ROBERT M. MONCRIEF. Bofluis thompsmn (Fowler)
1923, a valid species of flatfish (Pisces; Bothidae) from the Hawaiian Islands 237
Note
CABLE, WAYNE D., and WARREN S. LANDERS. Development of eggs and em- bryos of the surf clam, Spisida solidissima, in synthetic seawater 247
For sale bv the Superintendent of Documents. U.S. Government Printing Office. Wasliington. DC. 20402 - Subscription price: $10.85 per year (S2.75 additional for foreign mailing). Cost per single issue - $2.75.
CHEMICAL SIGNALS IN THE SEA: MARINE ALLELOCHEMICS AND EVOLUTIO
J. S. KiTTREDGE,'- FRANCIS T. TaKAHASHI,^
James Lindsey,^ and Reuben Lasker'^
ABSTRACT
Observations in chemical ecology suggest the coevolution of "natural products" of plants and the chemoreceptors of herbivorous insects. We have reviewed evidence which suggests that this coevolution extends back to the primordial protistans. Thus, the evolutionary pressure for the development of a chemosensory capability probably derived from the presence of metabolic products in the milieu. These products are considered to have been both cues to the location of prey and "membrane irritants" evolved in the initial phase of chemical protection. Sometime later this chemosensory capability provided several functions in the evolution of metazoans, i.e. the precursors of developmental signals, hormone function, and synaptic transmission.
We consider that most of the extant "natural products" of plants and marine invertebrates are protective allomones. A feature of allomone function that has been termed "antifeedant" or "feeding inhibitor" may represent the "cryptic odors" of Haldane. We provide evidence that the naphthoquinones with a juglone or naphthazarin structure have this activity. Octo- pus ink has a "cryptic odor" effect on moray eels. Marine Crustacea have, however, evolved an ability to perceive the orthoquinone precursors of the ink, a warning signal.
Evidence for an array of sex pheromones in a crab and a cycloid swimming pattern in a copepod that may enable it to follow a chemical gradient indicate the complexity of behavioral responses to chemical cues.
The earliest form of interaction between organ- isms was probably by means of chemical agents. This interaction involved both conflict and cooperation and its existence implies detec- tion of these agents. Haldane (1955) first suggested that chemical communication is the' most primitive form of communication, orgin- ating with primordial unicellular organisms. He reasons that this primordial protistan com- munication was a necessary prelude to the evo- lution of metazoans and thus is a lineal pre- decessor of synaptic transmission and hormone reception. This early chemical communication may have evolved as an accessory to the active transport mechanism of the cell membrane or as a "membrane sensitivity" to metabolic by-products (Wynne-Edwards, 1962). That a
' This work was supported by NSF grant GB-27703; ONR Contract N00014-7I-C-0103; NOAA Institutional Sea Grant 2-35 187; PHS NB 08599.
- Marine Biomedical Institute, University of Texas Medical Branch, Galveston, TX 77550.
3 Zoology Department, Oregon State University, Corvallis, OR 97331.
* Department of Biological Sciences, University of California at Santa Barbara, Santa Barbara, CA 93106.
5 Southwest Fisheries Center, National Marine Fisheries Service, NOAA, La Jolla, CA 92037.
more detailed understanding of transducer physiology is central to further advances in neurobiology has been emphasized by Delbriick (1970). He considers the stimulus-response system represented by chemoreception or synaptic transmission to be homologous.
We wish to examine some of the recent con- cepts of chemical ecology and to present examples from the marine environment. Studies of chemoreception are providing evidence for the pervasive function of chemical signals in the environment. The "membrane sensitivity" concept of Wynne-Edwards may provide a clue to both the initial evolution of a transducer function and the continuing evolution of receptor sites of greater diversity and specificity. It is evident that this diversity has resulted from a continual interplay of chemical counter- measures and the development of neurosensory and behavioral adaptations to these agents.
ALLELOCHEMICS
At all levels of life we are finding examples of attack, defense, and behavioral response
Manuscript accepted July 1973.
FISHERY BULLETIN: VOL. 72, NO. 1, 1974
1
FISHERY BULLETIN: VOL. 72, NO. 1
based on chemical agents. These interactions and the characterization of the chemical agents involved are the subject of the newly developing field of chemical ecology (Sondheimer and Simeone, 1970). Chemicals that are syntheized and released by one individual of a species to alter the behavior of other members of the species are termed pheromones. These signals range in their function from trail markers and territorial markers through alarm and defense signals to those which control caste structure in social insects and the sex pheromones that are calling signals and aphrodisiacs. Chemicals also have a wide range of interspecific interactions. A substance produced by one organism may influence the behavior of members of other species. A flower scent that enhances pollina- tion is a well-known example. This field of chemical ecology has been termed allelo- chemics, and the chemical agents have been subdivided on the basis of function into allo- mones, which give adaptive advantage to the producing organism, and kairomones, which give adaptive advantage to the receiving organism (Whittaker and Feeny, 1971). The allomones include the repellents produced by many plants and animals, suppressants which inhibit competitors (e.g., fungal antibiotics), venoms, inductants (e.g., gall producing agents), and attractants (e.g., chemical lures). The kairo- mones include attractants (e.g., the scent of a prey), inductants (e.g., the factor that stimulates hyphal loop development in nematode-trapping fungi), danger signals (e.g., predator scents, secondary plant substances indicating toxicity), and stimulants (e.g., hormones that induce growth in the receiving organism).
The diverse natural products, coumarins, quinones, flavonoids, acetylenes, terpenoids, saponins, cardiac glycosides, alkaloids, thiols, and cyanogenic glycosides, which were long considered metabolic waste products, are now recognized to be allelochemic agents. Examina- tion of the function of these natural products provides some insight into their evolution. Some of these compounds are toxic, some are chemical lures, others inhibit the growth of competitive plant species, but the bulk of these compounds probably function as "feeding inhi- bitors" of herbivores (Gilbert, Baker, and Norris, 1967; Munakata, 1970). The coevolution of butterflies and plants is considered by Ehrlich and Raven (1964). They emphasize the role
of reciprocal selective responses during this evolution and conclude that "the plant-her- bivore interface may be the major zone of inter- action responsible for generating terrestrial organic diversity." The "accidental" evolution of a metabolic sequence resulting in the produc- tion of a noxious substance by a plant provided a selective survival advantage in the clone carrying this capability. Decreased predation by herbivores on those individuals containing the highest concentrations of the new sub- stance resulted in genetic selection for increased synthesis and storage of the noxious substance. Such "protected" species experience an explosive increase because of their protection from contemporary phytophagous organisms. The first evolutionary response of the her- bivores must have been the development of the capability to detect the compound, i.e. sensitive external chemoreceptors. Later evolutionary events led to the development in some indi- viduals of a tolerance for the noxious substance. The herbivores which developed this tolerance then had access to a large food supply for which there was no competition. The ability to detect the substance then had an altered function, the feeding inhibitor was now a feeding stimulant. The present evidence of the repeated occur- rence of this cycle is the existence of tightly coupled herbivorous insects and their host plants, presumably arising through coad- aptation.
In 1955 Haldane, in a consideration of chemical communication and visual signals, wondered if cryptic odors had ever evolved. While most of the feeding inhibitors that have evolved are probably irritants, many may be cryptic odors. It is likely that the two activities may only differ in the membrane affected. The term irritant implies membranic sensitivity and, of those membranes of an organism in immediate contact with the environment, the chemosensory membranes are likely the most sensitive to chemical irritation. In an environ- ment in which a major fraction of the informa- tion flow is chemical, any agent capable of disrupting the chemosensory organs of a preda- tor would provide an ideal mechanism for "hid- ing" from that predator. Cryptic odors may be either "negative odors" altering, for protracted periods, the membrane potential of the dendrites and blocking their normal generator potential, or they may be the chemical equivalent of a
KITTREDGE ET AL.: CHEMICAL SIGNALS IN THE SEA
"white noise," producing an "uncoded" array of spikes in the chemosensory neurons.
The best description of behavior suggesting a "cryptic odor" in the marine environment is that given by MacGinitie and MacGinitie (1968). The ink of an octopus is considered a "smoke screen"; however, it can also affect the olfactory sense. The MacGinities observed that after a moray eel swam through the ink cloud of an octopus it could no longer "recognize" an octopus. The moray eel apparently requires both visual and olfactory input for this recogni- tion. They state, "We were surprised to find that the real effect of the ink of an octopus is to paralyze the olfactory sense of its enemies." The melanin of the ink is a polymer of oxidized L-DOPA. The polymerization proceeds through three orthoquinones, dopaquinone (6, Figure 1), dopachrome (7), and indole-5, 6-quinone (8). In the biosynthesis of melanin, this oxidation is catalyzed by polypheny 1 oxidases; however, heavy metal ions can also catalyze the oxidation, and it can be readily demonstrated that the trace of heavy metal ions in seawater will rapidly convert L-DOPA to melanin. The octopus ink loses its potency with time, a factor that would indicate that the biological activity of the ink is due to the presence of the unstable monomer orthoquinones in the fresh ink (Kittredge, Takahashi, and Lindsey, unpublished data).
The observation of Gilbert et al. (1967) that juglone (5-hydroxy-l,4-naphthoquinone) (1. Figure 1) is a deterrent to feeding by the bark beetle, Scolytus multistriatus, suggested a similar function for the polyhydroxynaphtho- quinones occurring in the echinoderms. These spinochromes are all derivatives of juglone (1) or naphthazarin (2). They occur as soluble salts in the tissues and may be present in considerable amounts in the larvae. They also occur as insoluble calcium salts in the spines and tests (Thompson, 1971). The echinoids have received the closest attention, but P. J. Scheuer and his group have demonstrated the presence of these compounds in the other four classes of this phylum — the holothurians, asteroids, ophiuroids, and crinoids (Singh, Moore, and Scheuer, 1967). They also demonstrated the presence of a substituted 2,5-benzoquinone (3) in the genus Echinothnx (Moore, Singh, and Scheuer, 1966). The crinoids are interesting in that they contain primarily a series of poly- hydroxyanthroquinones (e.g., rhodocomatulin,
OH 0 I II
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Figure 1. — Structures of compounds typical of those which may function as "cryptic odors." (1) juglone. (2) naphthazarin, (3) 2, 5-dihydroxy-3- ethylbenzoquinone, (4) rhodocomatulin, (5) fiavone, (6) dopaquinone, (7) dopachrome. (8) indole-5, 6-quinone.
4) (Sutherland and Wells, 1967; Powell, Suther- land, and Wells, 1967; Powell and Sutherland, 1967; Matsuno et al.. 1972; Erdman and Thomson, 1972).
Utilizing the "feeding response" of the lined shore crab, Pachygmpsus crassipes, which consists of a rapid lateral movement of the mouthparts when presented with a feeding stimulus, we have bioassayed the "feeding inhibitor" activity of juglone and eight repre- sentative spinochromes. The "feeding stimulus" was a 20-iul aliquot of a 3-mM solution of taurine in seawater administered from a repeat- ing syringe close to one of the antennules of the crab. Initially the crabs were immersed in a l-/uM solution of the naphthoquinone and tested for a feeding response. Five experimental and
FISHERY BULLETIN: VOL. 11. NO. 1
one control crab were utilized for each compound. No feeding responses were observed in any of the test crabs while all of the controls were positive. A second series of bioassays was designed to determine the onset of inhibition. The crabs were placed in seawater and stimu- lated with 20 fji\ aliquots of a solution of 3 mM taurine and 1 jliM quinone. The stimulus was administered at 2 sec intervals to alternate antennules. Inhibition of the "feeding response" was observed at approximately 10 sec. The naphthazarin derivatives were apparently more potent than the juglone derivatives. We interpret these results as indicative of a "cryptic odor" function; the crabs cannot detect the feeding stimulant after a brief exposure to the quinone.
Many higher plants contain juglone or other hydroxynaphthoquinones or benzoquinones. These compounds also occur in fungi, lichens, pholangids, millipedes, and insects. 1,4-benzo- quinones are the most common ingredient of insect defensive secretions and the 2,5-sub- stituted 1,4-benzoquinones are characteristic of fungi. A similar "cryptic odor" function may be predicted for these compounds.
Norris (1969) compared the feeding deterrent activity of a number of substituted naphthoquin- ones. Juglone (1) and naphthazarin (2) were the most potent inhibitors. The apparent effective- ness of the hydroxy groups in the 5- or 5,8- positions in these naphthoquinones suggests an examination of the function of the major group of secondary plant metabolites, the flavones (5) (Harborne, 1972) which have a marked structural similarity.
Whittaker and Feeny (1971) predict "that research into the relations of multicellular marine algae and their consumers will reveal chemical defenses and responses paralleling those of higher plants and animals on land." The most likely candidates to fulfill this predic- tion are the highly halogenated hydrocarbons that are synthesized by algae and stored in the tissues of the herbivorous gastropod, Aplysia caHfornica (Faulkner and Stallard, 1973; Faulkner et al., 1973). We would add to the prediction of Whittaker and Feeny that research- into the relations of many marine inverte- brates and their predators may reveal allomones. Some of the "natural products" of marine invertebrates that have been recently character- ized and that may have this function are the halogenated antibiotics that have been isolated
from, sponges (Sharma, Vig, and Burkholder, 1970; Fattorusso, Minale, and Sodano, 1972; Moody et al., 1972; Anderson and Faulkner, 1973). Steroid saponins that are toxicants or irritants have been characterized from holo- thuroids and starfish (Yasumoto, Nakamura, and Hashimoto. 1967; Tursch et al., 1967; Roller et al., 1969; Tursch, Cloetens, and Djerassi, 1970; Turner, Smith, and Mackie, 1971).
We recall a simple demonstration by the late C. F. A. Pantin of the sensitive chemo- sensory capability of sea anemones for saponin. The nematocysts of sea anemones require both a mechanical and a chemical stimulus for discharge. One can brush the surface of a sea anemone's tentacles with a clean glass rod without effecting any discharges. If, however the glass rod is first dipped into a dilute saponin solution, a massive discharge is effected.
An observation by Clark (1921) suggests the existence of allomones in crinoids. He discusses the avoidance of comatulid crinoids by fish and suggests the activity of glands at the base of the tentacles. The comatulids are unique in containing both polyhydroxyanthro- quinones and aromatic polyketides (Kent, Smith, and Sutherland, 1970; Smith and Sutherland, 1971).
MARINE KAIROMONES
As in the terrestrial environment, in- vertebrates utilize chemical cues to locate hosts or to warn of predators. Davenport (1966) demonstrated the response of commensal poly- noid polychaetes to a "host factor" in the water draining from tanks containing the host species of starfish. In an electrophysiological analysis of the antennular chemoreceptors of two com- mensal shrimps. Ache and Case (1969) demon- strated the specificity of the response to "host water" from the specific hosts, Haliotis spp. and Stro)igyloceiitrotus spp.
Predatory starfish induce an escape response in a variety of molluscs (Feder, 1967), and these behavioral responses probably effectively reduce the predation on these species that can detect the predator (Feder, 1963). The active materials in extracts of the starfish Marthasteria glaciali.s and Asten'a.s nibcHs which induce the escape response have been shown to be steroid saponins (Mackie, Lasker, and Grant, 1968).
KITTREDGE ET AL: CHEMICAL SIGNALS IN THE SEA
The threshold for response by the snail, Biicc'nium uudatiim is 0.2-0.4 X lO"-' M (Mackie, 1970). and the structure of these steroid glycosides has been determined (Turner et al., 1971).
A behavioral bioassay of one of the ortho- quinones derived from L-DOPA, dopachrome, utilizing the feeding response of the lined shore crab PachygmpsHS crassipes indicated that this quinone might also be a "cryptic odor." Electro- physiological studies, however, demonstrated that these results were misleading. Utilizing a preparation of the dactyl chemoreceptors of the spiny lobster Pa)udinis interruptus, we detected chemoreceptors for this quinone that were about a hundred times as sensitive as the general amino acid receptors in this prepara- tion (Figure 2). While we have not explored the
range of specificity of these receptors, the results suggest that these crustaceans, the natural prey of the octopus, have evolved a mechanism for detecting the presence of the predator. Our results with the bioassay likely reflect a priority of responses to the two chem- ical stimuli (Kittredge, Takahashi, and Lindsey, unpublished data).
PHEROMONES
Unicellular chemical communication, analogous to Haldane's primordial protistan communication, is evident in the conjugation of ciliates. The microconjugant of a peritrichous ciliate, which is free swimming, can identify the macroconjugant, which is sessile, by chemicals released by the latter. Although evidence for
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Figure 2. — Electrophysiological recordings from the dactyl chemoreceptors of a spiny lobster, Panulims interruptus. (1) Seawater blank, (2) IQ-'i M dopachrome in seawater, (3) Persisting spikes in dopachrome receptors (continuation of 2), (4) 10-3 M taurine in seawater, (5) 10"3 M taurine after dopachrome and a seawater wash.
FISHERY BULLETIN: VOL. 72. NO. 1
the presence of a large number of agents chemo- tropic for male gametes exists (Machlis and Rawitscher-Kunkel, 1963). only two have been chemically characterized. Sirenin. the active compound produced by the female gametes of the water mold Allomyces, has been isolated and characterized as an oxygenated sesquiterpene (Machlis et al., 1966), and its structure has been uniquely established (Machlis, Nutting, and Rapoport, 1968). It is active in attracting male gametes at 10"'"M. The corresponding work from the marine field resulted in the characterization of the active substance released by the female gametes of the brown alga Ectocarptis siUckIosk.'^ as allo- cis-l-(cycloheptadien -2', 5'-yl)-butene-l (Miiller et al.. 1971). The receptor sites on the male algal gametes evidence a low level of specificity. Many lower hydrocarbons, esters, alcohols, and aldehydes, at higher concentrations, will mimic the natural compounds in attracting male gametes (Cook, Elvidge, and Bentley, 1951; Miiller, 1968; Hlubucek et al., 1970).
Though many efforts to demonstrate a chemo- tactic response by mammalian sperm to sub- stances from eggs have yielded negative results, such attraction does occur in marine forms. Sperm of the thecate hydroids Cai)ipanularia flexuosa and C. calceolifera respond to a sub- stance issuing from the aperture of the female gonangium. The response is species specific (Miller, 1966). Observations by Dan (1950) suggest the activity of a similar substance from the eggs of the medusa Spirocodan saltatrix on the sperm of this species. The first examples of sperm chemotaxis in vertebrates are described in pai)ers on fertilization in the herring Clnpea by Yanagimachi (1957) and in the bitterling Acheilognathus by Suzuki (1961).
The attraction of the amoeboid form of the slime mold Dictyostelium discoideum during the aggregation phase which results in the formation of a multicellular "slug" represents the best studied protistan communication. The attractant is cyclic adenosine monophosphate (Konijn et al., 1968; Barkley, 1969). Pulses of cyclic AMP radiate out through the soil moisture at 5 min intervals from the center of a growing aggregation. The gradient and the pulse nature of the signal are maintained by each inward streaming amoeba. Each amoeba secretes a phosphodiesterase to break down the cyclic AMP and, on sensing a pulse of cyclic
AMP, emits its own pulse of cyclic AMP about 15 sec after receiving a signal (Cohen and Robertson, 1971; Robertson, Drage, and Cohen, 1972). Bonner (1969) has indicated the likely course of the evolution of this communication in the social slime molds. Soil bacteria, the food of the solitary predecessors of the slime mold amoeba, secrete cyclic AMP. It is reasonable to assume that a mechanism which initially increased the feeding success of these amoebas developed, due to selective pressure, the requi- site high sensitivity of response to a chemical signal necessary for aggregation. This capacity then facilitated the evolution of the social species. This is very close to Haldane's premise of the evolution of chemical communication prior to the evolution of metazoans. In further support of Haldane's premise of the lineage of hormones, after aggregation is complete the "metazoan" slug phase migrates to the soil surface and then certain cells differentiate into stalk cells which will eventually support the spore head. Cyclic AMP is apparently the chemical signal for the developmental differ- entiation of some cells into stalk cells (Bonner, 1970).
The recent rapid growth of our understanding of pheromone communication in insects was founded on half a century of acute biological observations which implicated the existence of chemical messengers. The isolation and chemical characterizations of a growing number of pheromones, and the concomitant behavioral studies, have provided the basis for our appreciation of the role of chemical communica- tion in the life cycle of many species. Among the many recent reviews are those of Beroza (1970) and Jacobson (1972). Electrophysiological investigations of chemoreception in insects have demonstrated that the receptor cells may be divided into two groups, either "specialists" or "generalists" (Yamada, 1970). Among the "specialists" are the pheromone receptors and the receptors for specific secondary plant sub- stances that act as phagostimulants (Schoon- aoven, 1968). While remarkable success has been achieved in recording the response of single receptor cells as well as the summed receptor potential of all the antennal chemore- ceptors (electroantennogram) these workers have had to contend with a technical problem inherent in studies with this material. Evalua- tion of the response of a chemosensory organ
KITTREDGE ET AL: CHEMICAL SIGNALS IN THE SEA
or a single cell is difficult when the stimulant must be presented in the gas phase. Each species of stimulant molecule must partition between the gas phase and an aqueous film. The active concentration at the receptor membrane is unknown. A study of the physi- ology of pheromone reception by aquatic organ- isms would avoid this limitation.
A survey of the literature reveals that, as in the field of entomology, there exists a broad basis of behavioral observations suggesting the role of chemical communication in the aquatic environment. These studies suggest that marine invertebrates are primarily dependent on chemo- reception for information from their environ- ment. The input is composed of a broad spectrum of chemical messages ranging from species specific pheromones eliciting stereospecific responses, e.g., mating behavior, epidemic spawning, aggregation, or alarm behavior, through those kairomones triggering metamor- phosis or migration to the cues indicating the proximity of predators or prey.
The closest parallel to insect pheromone communication observed in marine organisms are the sex pheromones of marine Crustacea. The first experimental demonstration of "chemical recognition" by marine Crustacea is the description of the behavior of male copepods (Labidocem aestiva) by Parker (1902). In a series of elegantly simple experiments he demonstrated that "they [the females] probably give rise to some substance that serves as a scent for the males; in other words, the males are probably positively chemotropic toward the females." Moreover Parker noted that "they [the males] seldom pass near the tube without some characteristic reaction. Usually they made one or two quick circles as they swam by, or even a somersault-like motion; these were observed fifteen times when the females were in the tube, never when they were not." Lillelund and Lasker (1971) observed similar swimming behavior in male Labidocera joUae. Although L. joUae females swim in a seemingly random pattern with only occasionally looped excursions, the males frequently vary their random course of a few seconds duration by swimming in circles, covering a small area intensively. Of greater interest was the observation that rather than circles, the path of the males often resembled a curtate cycloid. The males occasionally pro- gressed for several centimeters in this curtate
cycloid path (Figure 3). These observations, although obtained during feeding studies, suggest an important aspect of the physiology of pheromone response in small Crustacea — the mechanism of sensing a chemical gradient. Crisp and Meadows (1962) have stated that, because of the small distance between the chemosensory organs of barnacle cyprid larvae, these larvae cannot detect a chemical gradient and thus
1 cm I 1
Figure 3. — Swimming behavior of a male copepod Lahidoceru jollae. A' and B' mark the termini of the tracings. The upper trace shows both an occasional circu- lar swimming course, progression in a curtate cycloid course and "doubling back." The lower trace is an extreme example of the "doubling back" behavior.
FISHERY BULLETIN: VOL 72. NO 1
cannot exhibit chemotactic behavior. This reasoning has been applied to all small marine Crustacea including copepods. From the above observations it is apparent that the reasoning of Crisp and Meadows is invalid for Labidocera and probably for other small Crustacea. The critical dimension is the diameter of the circular course, not the dimensions of the organism. A circular swimming i)attern in a concentration gradient of a stimulant would result in a sinus- oidal variation in the signal intensity. Altera- tion of the radius of curvature of the swimming course in response to this sinusoidal input would result in cycloidal progression in the gradient. It appears from the observations of the behavior of male L. jollae in the feeding experiment that a threshold level of stimulant will trigger a circular swimming pattern, if this circular course results in the detection of a gradient, the circular course will become a curtate cycloid with the ratio of the major to the minor radius being a function of the intensity of the gradient. A frequent observation is a doubling back. If several progressions of the cycloid result in loss of the gradient signal (as must frequently occur in a medium in which the dimensions of the turbulent flow are of the same scale as the swimming pattern), the swimming plots indicate that the male Labido- cera can effectively loop back through the area where the signal was initially detected (Figure 3). These observations indicate some power of spatial orientation and short term memory in Labidocera.
In crabs the male is attracted to the premolt female. During this attraction phase he may display a stance characterized by standing on the tips of his dactyls and elevating his body. He will seize the premolt female and place her below his body. He will protect her during the vulnerable molting period and they copulate immediately after molting. Ryan (1966) demon- strated pheromone communication in this inter- action. Water from a tank containing a premolt female Portunus sanguinolentus, when added to a tank containing a male of this species, elicited the premolt stance. Evidence that the pheromone is released from the antennule glands was provided by sealing these glands and noting the absence of the stimulating factor.
We have examined this pheromone com- munication in the lined shore crab, Pachygrap- sus crassipes. We isolated an active substance
and found that it behaved chromatographically like the molting hormone, crustecdysone. Pure crustecdysone is active in stimulating all of the precopulatory behavior of male lined shore crabs from an early search behavior through the display stance to seizing the female. The thresh- old for stimulating the stance is 10''^ M (Kittredge, Terry, and Takahashi, 1971). Con- firmation of the identification has been obtained by injecting tritiated crustecdysone into inter- molt female Dungeness crabs (Cancer niagister) and detecting its release as the females entered premolt. Recently we have detected the presence of two additional pheromones released by the female lined shore crabs. Compound A is released in addition to crustecdysone prior to molt. After molting compound A is no longer released into the water, but, if the female is held in isolation from male crabs, a second compound, B, is re- leased. It is likely that the postmolt female has a different message to transmit.
Evolutionary biologists concerned with the inception of pheromone communication have long been puzzled by a dilemma. This chemical communication implies two new capabilities, that to synthesize a messenger compound and the ability to receive the message and trans- late it into a behavioral response. The improb- ability of the simultaneous occurrence of these two de novo events suggests a stepwise sequence. The observation that the molting hormone of Crustacea can function as a sex pheromone indicates that the primordial Arthropoda, through an evolutionary sequence that resulted in structuring the receptor site for the hormones on chemosensory membranes, were able to initiate pheromonal communication (Kittredge and Takahashi, 1972).
SUMMARY
Evidence from the literature supports Haldane's premise that chemical communica- tion is the most primitive form of communica- tion and thus the lineal predecessor of synaptic transmission and hormone function. Trans- ducers of environmental chemical information have likely evolved in response to the metabolic products released by their prey and by competi- tive organisms. This coevolution of "natural products" and the respective transducers has existed from the earliest metabolic product that happened to be a membrane irritant to the
8
KITTREDGE ET AL: CHEMICAL SIGNALS IN THE SEA
present. We thus consider it likely that most of the "natural products." not only of terrestrial plants, but also of marine plants and inverte- brates, function as allomones, kairomones, or pheromones. Faulkner and Anderson (In press) have provided a review of the chemistry of the "natural products" of marine organisms.
Conceptually, in such a "chemical environ- ment" the most effective protection from a predator would be a "cryptic odor," an irritant that disrupts chemoreception. These cryptic odors may be released into the environment, as is the active component of octopus ink, they may exist in the epidermal tissues or glands where they would function at the inception of attack, or they may be contained in the eggs or larvae. Most sessile marine invertebrates re- produce by epidemic spawning, the simultan- eous release of the gonadal products of an entire local population of a species. Most sessile marine invertebrates are also filter feeders. The prime advantage of epidemic spawning is the enhancement of fertilization. However, in the densely populated benthic environment, a heavy loss of eggs or larvae to filter feeders may occur. The presence of a "feeding inhibitor" in the eggs or larvae would reduce such losses. Reiswig (1970) reported that they observed epidemic spawning of the sponge Neofibiilana iiolitaiigere on a Jamaican reef. At the time they were measuring the water pumping rate of other sponges. When the epidemic spawning of A^ nolitangere started, the pumping rate of the. species under study, Vero)igia sp, abruptly decreased and remained negligible for 2 days. A', nolitangere is known to contain toxic sub- stances.
The evidence for chemical cooperation, from gamones to sex pheromones, suggests a pattern of increasing complexity in the function of chemical cues. The behavioral response of even a "simple" crustacean to a chemical gradient appears to involve at least some short term "memory" or a type of "chemical-spatial" sense that we have not observed in such clear- cut form in any other organism.
The study of the chemical ecology of the marine environment is scarcely in its infancy. The chemical characterization of some of the intraspecific and interspecific messages in the sea and the physiology of their perception are challenges. Solutions to these paired problems
will provide insights into the evolution of chemical transduction and perhaps expose a hierarchy of perception from membrane irritation to synaptic transmission.
ACKNOWLEDGMENTS
We wish to acknowledge the contribution of Paul J. Scheuer, Department of Chemistry, University of Hawaii, to the study of the "cryptic odor" activity of natural marine naphtho- quinones. He generously provided eight spino- chromes and contributed observations on their structure and occurrence.
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11
A SIMPLE BIOECONOMIC FISHERY MANAGEMENT MODEL: A CASE STUDY OF THE AMERICAN LOBSTER FISHERYi
Richard F. Fullenbaum^ and Frederick W. Bell-* ABSTRACT
The pressures of world economic expansion have led to more intensive exploitation of living marine resources as a source of protein. The exploitation of these common property resources leads, in many cases, to overfishing and depletion. This paper attempts to develop a simplified management tool to prevent overexploitation and depletion of a fishery resource. A general resource model is postulated embracing both biological and economic relationships. This bioeconomic model approximates the operation of a fishery under free access to the resource. A Schaefer type yield function is combined with a linear demand function, and other standard economic relationships and simulations are performed to evaluate the model. Using computer simulation, we imposed five management strategies on the case example, the American lobster fishery. These strategies include (1) freezing fishing effort by raising license fees: (2) reducing fishing effort to that necessary to harvest at the maximum sustainable yield by raising license fees: (3) reducing fishing effort to an "economic optimum"" where marginal cost of doing business is equal to marginal revenue from sales by raising license fees: (4) instituting a "stock certificate plan"" where individual fishermen would own portions of the resource and trade catch certificates on the open market: however, the total number of catch certificates would not exceed the maximum sustainable yield: and (5) doing nothing. The economic impact in terms of catch, fishing effort, number of fishermen, ex-vessel prices, license revenues, and returns per boat and fishermen were computed for each management strategy so that policymakers and industry leaders could see the alternative consequences of these management positions. The simplified model also is available for use in evaluation of other management schemes that might be suggested.
In the past few years the world community has become increasingly aware of the sea and its resources. The pressures of world economic expansion have led to more intensive exploita- tion and, at the same time, to increasing con- cern over the marine environment. Many man- agement strategies used to protect these re- sources from overexploitation have resulted in inefficient use of gear and equipment as shown by Crutchfield and Pontecorvo (1969). The purpose of this paper is to develop a bioeconom- ic model of living marine resource exploitation which can be used to assess the economic im- pact of alternative management strategies for the U.S. inshore American lobster fishery. The U.S. American lobster fishery is a classic
case of rapid increases in consumer demand impinging upon a limited resource (Bell. 1972). It should be made quite clear that this analysis is intended to predict the effects of alternative actions without recommending any specific policy.
SPECIFICATION OF THE GENERAL RESOURCE USE MODEL
Before we are able to evaluate the economic impact of various management strategies, it is necessary to develop a general bioeconomic model of how a fishery functions. The following general model has been developed by Fullen- baum, Carlson, and Bell (1971):
' This article was first submitted for publication 7 August 1972. At that time, all data were as current as could be obtained for purposes of the analysis. The views of the authors do not necessarily represent the official position of the U.S. Department of Commerce.
2 Executive Office of the President, Office of Manage- ment and Budget, Washington, DC 20503.
3 Formerly of Economic Research Division, National Marine Fisheries Service, NOAA: present address, Florida State University, Tallahassee, FL 32306.
or
X = f{X, Kx) Kx = Kg{X, K) X =giX,K) C =Kn
(1) (2)
(3) 13
Manuscript accepted June 1973.
FISHERY BULLETIN: VOL. 72. NO. 1. 1974.
FISHERY BULLETIN VOL. 72, NO. 1
TT = pKx -C = pKgiX,K) -Kn (4)
5 277', 7r<0
(5)
In the above system, X is the biomass; K equals the number of homogeneous operating units or vessels; x is the catch rate per vessel; C is total industry cost (in constant dollars) or total annual cost per vessel multiplied by the number of vessels; ^ is equal to total annual cost per vessel (in constant dollars) or opportunity cost;' 77 is industry profit in excess of oppor- tunity cost; p is the real ex-vessel price; and 5 J , 5 2 represent the rates of entry and exit of vessels, respectively. Equation (1) represents the biological growth function in which the natural yield or net change in the biomass {X) is dependent upon the size of the biomass, X, and the harvest rate, Kx. X reflects the influence of environmental factors such as available space or food, which constrain the growth in the biomass as the latter increases. The harvest rate or annual catch, Kx, summarizes all growth factors induced by fishing activity. Equations (2) present the industry and firm production function for which it is normally assumed that
dg dX
= g,>0 and f^=g^<0:^
dg bK
In other words,
catch per vessel increases when the biomass increases and declines when the number of vessels increases. Equations (3) and (4) are the industry total cost and total profit function, respectively. Equation (5) is a very important equation since it indicates that vessels will enter the industry when excess industrial profits are greater than zero (i.e., greater than that rate of return necessary to hold vessels in the fishery, or the opportunity cost) and will leave the fishery when excess industrial profits are less than zero (i.e., below opportunity cost).
■* Opportunity cost is defined as the necessary payment to fishermen and owners of capital to keep them employed in the industry or fishery compared to alternative employ- ment or uses of capital.
■'•In some developing fisheries, it is possible that .i;2>0. For example, in the Japanese Pacific tuna fishery, inter- communication between vessels may increase the catch rate as more vessels enter the fishing grounds.
The equilibrium condition for the industry (n = 0) may be formulated as shown below:
P =
77
g{X,K)
(6)
Equation (6) merely stipulates that ex-vessel price is equal to average cost per pound of fish landed (i.e., no excess profits).
There are two important properties of the system outlined in (1) - (5). First, the optimum size of the firm is given and may be indexed by 77. Thus, the firm is predefined as a bundle of inputs." Second, the long-run catch rate per ves- sel per unit of time is beyond the individual firm's control." It is, in effect, determined by stock or technological externalities.** Finally, we are assuming that the number of homo- geneous vessels is a good proxy for fishing effort. Alternatively, we may employ fishing effort directly in our system by determining the number of units of fishing effort applied to the resource per vessel. This will be discussed below.
A QUADRATIC EXAMPLE OF THE RESOURCE USE MODEL
By combining the more traditional theories depicting the dynamics of a living marine re- source with some commonly used economic relations, we may derive a quadratic example of the general model specified above. This example effectively abstracts from complications such as ecological interdependence and age- distribution-dependent growth of the biomass on the biological side and, furthermore, assumes the absence of crowding externalities (i.e., ^2 ~ 0) in the production function on the economic side.
'' In other words, because we are dealing with a long-run theory of the industry, we are assuming that variations in output result from the entry or exit of optimum-sized homogeneous vessels.
^ We have implicitly assumed that such short-run changes as longer fishing seasons, etc., are all subsumed in a long-run context. Normally longer fishing seasons, for example, do not change catch rates per unit of time fished; nor do they change costs per unit of time fished. They do, however, change the effective level of K.
* A technological externality exists when the input into the productive process of one firm affects the output of another firm. In the context of fishing, an additional firm or vessel entering the fishery will utilize the biomass (as an input) and, as a result, in the long run will reduce the level of output for other vessels in the fleet. (See Worcester (1969)).
14
FULLENBAUM and BELL: AMERICAN LOBSTER FISHERY
The dynamics of a fish stock may be depicted by the logistic growth function (Lotka, 1956).^
X(t) =
1 + Ce
-KLt
where L>0,O0,/e>0, (7)
Kx = rKX
(11)
where r is a technological parameter.'- Finally, the total revenue function for the industry may take the following form:
where L, C, and K are assumed to be environ- mental constants. Differentiating (7) and sub- stituting we obtain,
X = ^ = kLX - /v'X2 = aX - 6X2 (g)
at
where
a = kL, b = k.
If (8) is set equal to zero, we may solve for the nonzero steady-state biomass, alb (i.e., L). Alternatively, the limit of X{t) as f ^ °° yields identical results. The maximum of (8) occurs when X is equal to al2b. Thus
max 3^ = a^l4b
(9)
The introduction of fishing (i.e., harvest or Kx) is assumed to have no interactive effects, so that the instataneous growth rate is reduced by the amount harvested:'"
^ = gX - 6X2 - Kx. at
(10)
The economic component of the model re- quires the exact specification of an industry production function and an industry revenue relationship. One hypothesis regarding the fish catch is that the proportion of the biomass caught is a direct function of the number of vessels (or equivalent fishing effort) exploiting a given ground." Thus, the total harvest rate is given as.
"Graham (1935) was the first biologist to apply the logistic growth model to exploited fish populations.
'" Schaefer, (1954) was the first population dynamicist to develop the function specified in equation ( 10).
'• Alternatively, one could assume that the proportion of the biomass caught declines as the number of vessels increases:
Kx = [\ - (\ - nf^]X.
0<f<l
With this specification, ; represents the proportion of the biomass taken by the first vessel and also represents the percentage taken by each succeeding vessel of the remain- ing biomass. This form was first developed by E. W. Carl- son (1970. An economic theory of common property re- sources. Unpubl. manuscr. Econ. Res. Lab., Natl. Mar. Fish. Serv., NOAA College Park, Md.).
pKx = (a- (iKx)Kx.
(12)
Equation (12) merely stipulates that the total revenue is a quadratic function of total landings, Kx. Dividing through by Kx will give us the familiar demand function where ex-vessel price is inversely related to landings, holding all other factors constant.'-'^ With total costs equal to Ktt, the profit function becomes
77 = (a - iiKx)Kx - Krf.
(13)
Given these formulations, the system in (10) - (13) can be reduced to two steady-state func- tions. The first, which condenses all relevant biotechnological factors, is the ecological equilib- rium equation. It plots the relationship between the biomass and the number of vessels (or fish- ing effort) needed to harvest the yield such that the biomass is in equilibrium. We can derive this equation by setting X equal to zero, sub- stituting (11) into (10), and solving for K in terms of X.-
K = -{a- bX).
(14)
Similarly, the second equilibrium function plots the relationship between X and A' under a zero profit state, i.e., under conditions that K — 0, or that there is no entry to or exit from the fish- ery. Thus, by setting (13) equal to zero and substituting (11) into (13), we obtain
K =
a
drX ^V2X2
(15)
'•^ A reviewer ot this article has pointed out that ; is not likely to be constant over any large number of years. Since there are no time series observations on X, r cannot be tested to see whether it varies over time or is a constant. In this case, we are merely following the simplified Schaefer model.
13 Such complicating factors as per capita income and its influence on ex-vessel prices can be introduced later as changes in the parameter, q.
15
FISHERY BULLETIN VOL. 72. NO. 1
These two curves are plotted in Figure !.'■♦ Their intersection at (X*, K*) denotes bio- economic equilibrium. The direction of the arrows describes the qualitative dynamic changes of a point in ])hase space. Figure 1 rep- resents the general case of exploitation. When (15) is combined with (14), however, we can simulate either nonexploitation (Figure 2) or extinction as a possible dynamic result (Figure 3).'-'' The state of the fishery — exploited, unex- ploited, or extinct — depends upon the para- meters a. b, r, /3, TT, and a and their interrela- tionships. This completes our general model of how a fishery functions. Now let us turn to a specific application of the model.
AN EMPIRICAL CASE STUDY:
THE U.S. INSHORE AMERICAN LOBSTER EISHERY
The U.S. inshore American lobster fishery — principally located off the coast of Maine — represents a good case study for a number of reasons. First, the American lobster is consid- ered a high quality seafood item and is a popu- larly consumed species for which demand has been increasing rapidly (Bell, 1972). Second, be- cause of intensive fishing pressure, the resource
''• In steady state, the reader should be aware that we have not constrained the population stock to its initial size or any other size. Using the Schaefer model (i.e., steady state), the stock size varies inversely with fishing effort, T. Even in a dynamic context, the biomass would asymptotically approach the steady -state solution.
'■' It should be pointed out that Schaefer (1954) discuss- es economic transitional states which are very similar to the bioeconomic model presented in this paper. He states:
"To arrive at a particular function to describe the change of the intensity of fishing with the size of the population, we may consider that the incentive for new investment is proportional to the return to be expected, in which case there will be a linear relation between the percentage rate of change of fishing intensity and the difference between the level of fish population and its economically critical level, b. This function will, then, be
dF
where k-^is a constant."
b)
(11)
has shown signs of overexploitation."' Third, the inshore lobster fishery is one of the few grounds for which enough data are available so that some rough measures of needed biological and economic ])arameters can be derived. Fourth, according to Dow (1961),'^ the inshore lobster fishery is a relatively closed population as our production model assumes. Last, we believe that over the long run the American lobster population has not had a great divergence from the steady-state model employed in our analysis. The gross divergence from the steady-state assumption is significant only when fishing effort changes dramatically from period to period. For modest changes in fishing effort, the steady-state assumption will not yield biased estimates. A check on the fishing effort series for the American inshore northern lobster fishery reveals a steady and gradual increase. The alternative methods of Pella and Tomlinson (1969) do yield biased parameters due to nonlinear fitting methods. Gulland's (1961) method yields bia.sed parameters since effort is averaged and then used as an indepen- dent variable. Therefore effort in period t is not indei)endent of effort in period t -\- 1 which violates classical statistical assumptions under- lying least squares. Also the predictive value (using the steady- state assumption) or goodness of fit is certainly at an acceptable level, R"^ = 0.962 (infra). Our discussion will be subdivided on the basis of production-related and demand- related estimates.
The Production Eunction and the Supply of American Lobsters
There are four parameters on the supply side for which initial estimates are required: a, b, r.
His process of transitional states is implicit in our dia- grams in Figure 3 since adjustment (i.e., transitional states) will occur anywhere in phase space to the equilibri- um values where X = 0 and K = 0.
"* U.S. landings of trap-caught American lobsters in- creased from approximately 23 million pounds in 1950 to a peak of over 29 million pounds by 1957. Since 1957 landings have fallen off, reaching a low of 22 million pounds in 1967. In 1969 lobster production had recovered to 26.9 million pounds. Despite the poor performance of production over the 1950-69 period, the number of lobster traps fished per year (i.e., a proxy for fishing effort) has increased secularly from approximately 579,000 in 1950 to over 1,060,000 in 1969. Because of these past events, several bills have been presented in the Maine Legislature to apply some sort of stringent licensing scheme to limit entry.
'^ Dow, R. 1971. Effort, environment, supply, and yield in the Maine lobster fishery. Unpublished manuscript sub- mitted to the U.S. Fish and Wildlife Service, Washington, D.C. 125 p. (May be obtained from Sea and Shore Fish- eries, Maine.)
16
FULLENBAUM and BELL: AMERICAN LOBSTER FISHERY
Figure 1. — Exploitation.
Figure 2. — Non-exploitation.
|
i |
|||
|
TT |
|||
|
\ K=-[a-bX] \ |
|||
|
\ |
>- |
Figure 3. — Extinction.
17
FISHERY BULLETIN VOL. 72. NO. 1
and 7r.'»* The first three can be developed by combining statistical estimation and indepen- dently derived data. Assume that the biomass is instantaneouslv in equilibrium (i.e., dX_^ q)
dt
Then, taking the inverse of (14) and substituting it for X in (11), we obtain:
(il2b, it follows that the following parameters may be estimated (designated by *):
Kx = cK- dK^
(16)
r = C/2X
b = [d/p2] -1
a = cblr.
(18) (19) (20)
where
and
C = J,d
If b
X = c - dK.
(17)
Equation (16) is the familiar parabolic yield function postulated by Schaefer (1954).'^ Notice that both the harvest rate, Kx, and output per vessel, X, may be specified solely in terms of the number of vessels or fishing effort. Similarly, the common property resource externality, as given in (17), is a function only of the level of K. Over a longer period of time the basic assump- tion underlying equations (16) and (17) may reflect a valid representation; i.e., effort or K is the only instrumental variable affecting out- put. There are three different parameters em- bedded in estimates of c and (/. The only way that 0, b, and r can be derived is if some inde- pendent biological information is given. More specifically, suppose that we have an estimate of the biomass consistent with maximum sus- tainable yield, call it X° . Since X° is equal to
Thus, (17) will be estimated subject to one modification concerning the introduction of an environmental variable. Several biologists, including Dow et al. (1961),-" have argued that a long-term trend of declining seawater tem- perature is partially responsible for the decline in U.S. coastal catches. -• It will be assumed in this study that seawater temperature (°F) affects the a term in the growth function so that,
^ = aCF)X-bX^,
(21)
where °F is equal to the mean annual sea- water temperature, in degrees Fahrenheit Boothbay Harbor, Maine, with .
9a
a( F)
a'>0.
Seawater temperature can easily be incorporat- ed into (17) in the following way:
c -dK + z( F),
(22)
"* An alternative approach suggested by Thomas (1970) uses the Beverton-Holt model in developing a yield/ recruit relationship. However, because a stock-recruit- ment equation is not specified, it cannot be incorporated •nl'> our bioeconomic model at this time.
"* The reader should recognize that it does not follow that (17) can be derived from a generalized growth equa- tion [X = F(X) - K\ = 0] and production function Kx = l\X,K). Only under certain specifications of the previous two functions will it follow that .v can be defined as a unique function of K (or X) only. In addition, this production function could have been more generally speci- fied as Kx - rK^XP. However, two compelling factors make it desirable to employ this function. First, there are no observations on the biomass, X, so that empirical tests cannot be made to estimate B. Second, the equation Kx = rKX combined with the logistic gives an excellent empirical fit to past behavior in the fishery (i.e., R- = 0.962 for yield function equation 23). In addition, Schaefer makes the same assumption as we did, and this assump- tion is generally accepted as plausible for most fisheries. In conclusion it is difficult for us to imagine how a differ- ent assumption could lead to superior predictive results (i.e., goodness of fit).
where z represents the change in output per boat as a result of a one-degree change in water temperature. --
Data on the number of traps fished per year for the entire inshore American lobster fishery
'-" Dow, R., D. Harriman, G. Ponlecorvo, and J. Storer. 1961. The Maine lobster fishery. Unpublished manuscript submitted to the U.S. Fish and Wildlife Service, Washing- ton, D.C. 71 p. (May be obtained from Sea and Shore Fisheries, Maine.)
-• Higher seawater temperature can affect the natural yield of lobsters by providing a climate in which molting is facilitated. A larger number of molts will tend, ccwris paribus, to increase the yield associated with any given level of the biomass.
-- Implicit in the way the effect of seawater temperature is measured is the relationship:
[a = <;o + d(°¥)].
18
FULLENBAUM and BELL: AMERICAN LOBSTER FISHERY
are available for the 1950-69 period (see Appen- dix Table).-^ Output per trap was regressed against the number of traps and seawater tem- perature on the assumption that the number of traps per boat was constant. The regression estimates yielded the following results:
X = -31.82 - 0.00002807(T) + 1.846(°F) (23)
(6.55)
(4.99)
R2 = 0.962 D-W = 2.38
where T = 562. 8( A'): d = 0.0156; c = - 31.82 + 1.846(°F). In (23). T is equal to the number of traps fished per year, and f-ratios are in parentheses.-^ Both T and °F are statistically significant at the 5% level and exhibit the cor- rect sign; the Durbin-Watson statistic indicates no significant autocorrelation.
The only step required to obtain the biotech- nological parameters is an estimate of the bio- mass consistent with ma.ximum sustainable yield. It has been calculated that (assuming a temperature of 46°F) the fishable stock of U.S. inshore American lobsters consistent with maximum sustainable yield is equal to 31 mil- lion pounds.'--^ For the Gulf of Maine (where most of the resource is located), estimates of the biomass were made through sampling experi- ments.'-*'
Finally, on the basis of recent cost studies, we have derived an estimate of n for 1966 equal
23 The assumption of a constant number of traps per boat is necessary in order to solve for a coefficient on "K". and thereby, to obtain the biotechnological paramet- ers embedded in the yield-effort relationship. The rela- tionship for 1966, derived on the basis of cost data ob- tained from the National Marine Fisheries Service's Divi- sion of Financial Assistance was 562.8 traps per full-time equivalent northern lobster boat. However, it should be pointed out that when the stock is large and the catch high, it may pay to increase the number of traps per boat: therefore, this might bias the number of "standard- ized boats", but not total amount of effort.
-'' However, the reader should note that the empirical estimates themselves (1950-69) make no assumption with respect to the relation between K and T. \ was regressed on T and °F. Only in the simulation was a relationship assumed (T = 562.SK).
-•^ U.S. Department of the Interior. 1970. Joint master plan for the northern lobster fishery. Unpublished man- uscript. 130 p. (May be obtained from the National Marine Fisheries Service, Washington. D.C.)
-6 No attempts were made to run the simulation model with varying sizes of the MSY biomass as this would un- necessarily complicate this paper which is intended to be simplistic as possible.
to $12,070.27,28 Therefore, on the supply side, the estimated parameters for 1969 are the fol- lowing:
a b r
1.85379
2.9899 X 10-^
5.1562 X 10-4
$13,191 (see footnote 27).
The Demand Function for American Lobsters
Only knowledge of d and /j is needed in order to complete the empirical component of the study. The estimation procedure is rather straightforward. We may specify the following demand function for all lobsters:
C
N
= F-m(P'/CPI) + g(y/AO
(24)
where C is equal to consumption of all lobsters, P' is the money ex -vessel price of American lob- sters, Y is aggregate U.S. personal income (1967 prices), A' is U.S. population, and CPI is the consumer price index. Since there are no exports of lobster, the following identity holds:
C = 1+ Q + Q.
(25)
where /, Q^, and Q^^ are the level of imported lobsters, U.S. production of all other lobsters, and U.S. production of inshore American lob- sters, respectively. Given (25), equation (24) may be solved in terms of P, or,
P =
CPI
If Qq, /, Y, CPI. and N are held constant, equa- tion (26) gives a unique relationship between the ex-vessel price of American lobsters and quantity landed.
Using data over the 1950-69 period (see Appendix Table), the parameters of equation (24) were estimated using least squares:
-' Cost data from the National Marine Fisheries Serv- ice's Division of Financial Assistance (1966) reveal the following cost breakdown for a representative lobster boat: operating expenses, $4,965.16: fixed expenses, $1,180.20: returns to capital and labor, $5,825.48. This gives a total of $12,070.84. The latter figure was updated to 1969 by income increases in Maine to obtain $13,191.
28 We will assume that rf remains constant in real terms. This is equivalent to keeping our estimate of it". Tf constant, while deflating all nominal variables on the demand side.
19
FISHERY BULLETIN VOL. 72. NO. 1
^= -0.0632 -0.005029(^j (2.06)
0.00051^ (27)
(5.38)
«2 = 0.816
D-W = 0.619
All of the independent variables are significant at the 0.05 level. However, the Durbin-Watson statistic indicates the strong possibility of posi- tive autocorrelation. Nonetheless, we will use these estimates as rough approximations to obtain the price-dependent relationship as shown in (26). Given 1969 values of exogenous variables (A^ - 199.100,000; Y - $567,635 million; CPI = 109.8 with a base of 1967 = 100; Q + I = 158.8 million pounds), we have.
P= 1.179 - (0.99853 X 10-^)Q.^.
(28)
Thus initial values for a (1.179) and ^ (0.99853 X IQ-^) have been obtained.-"
-9 For purposes of simplification, the parameters of the model are all assumed constant. Certainly, one could argue that the parameters, so tacitly assumed to be constants, are at best random variables. Therefore, a stochastic treatment might be used with criteria like maximal expected present value or minimal maximum expected loss for evaluating the management alternatives rather than simple deterministic computations. Possibly, the parameters are random variables and conditional on some of the suggested management alternatives. For example, freezing effort might accelerate /■, leading to shifts in season or age structure harvested, hence a change in ulh.
HOW THE MODEL WORKS: THE IMPACT OF CRITICAL VARIABLES
To illustrate the power of the model in ex- plaining the impact of changes in critical variables, we may derive initial quantitative estimates of the ecological equilibrium and economic steady-state functions. In this section we will illustrate the power of the model in explaining the impact of changes in critical variables. The year 1969 is selected for initial quantitative estimates of the ecological equi- librium and economic steady-state functions. Table 1 shows what happens to the value of {X*, K*) as well as the equilibrium harvest level. {Kx)*, when the following changes take place:
a) A 25% increase in opportunity costs of labor caused by the development of greater regional industrial activity;
b) A 25% increase in the supply of other lobsters traceable to the discovery of a new lobster ground;
c) A 5% increase in personal per capita income; and
d) A decrease in water temperature from 48° to47°F.
Notice that these changes are for illustrative pur- poses; however they do come about on a routine basis in the real world. Perhaps 25% changes in selected variables do not come about in one year so the reader can view the new equilibrium
Table 1. — The impact of exogenous shocks to the inshore American lobster fishery on the effort, catch, and biomass.
|
Vessels, |
Traps |
Catch |
Biomass |
|
|
full-time |
||||
|
equivalent |
||||
|
K* |
£* |
Kx* |
X* |
|
|
Nuinhcr |
Niiiiibcr |
Million |
poiiiuls |
|
|
Initial equilibrium (1969) |
1,936 |
1 ,089,000 |
28.56 |
28.62 |
|
(computed by model) |
||||
|
New equilibrium: |
||||
|
(a) Increase (25°o) in opportunity |
1,531 |
861,718 |
28.1 |
35.6 |
|
cost of labor |
||||
|
(b) Increase (25°o) in exogenous |
947 |
533,000 |
22.3 |
45.7 |
|
supply of lobsters |
||||
|
(c) Increase (5°o) in personal per |
2,182 |
1,228,310 |
27.4 |
28.0 |
|
capita income |
||||
|
(d) Decline in water temperature by 1° |
1,851 |
1,041,710 |
26.8 |
29.0 |
|
(e) Changes (a)-(d) simultaneously |
905 |
509,356 |
20.7 |
45.9 |
20
FULLENBAUM and BELL: AMERICAN LOBSTER FISHERY
positions shown in Table 1 to result over a period of years from the 1969 initial e(iuilibrium. We may incorporate all of the four changes given separately in (a) - (d) to ascertain their net impact. The strength of the simulation model is that we can study the separate and combined influences on the fishery of important variables. Because we have both positive and negative influences on fishing effort, it is likely to be such that complete extinction of a particu- lar species would be somewhat difficult.-'"
ECONOMIC IMPACT OF SELECTED MANAGEMENT ALTERNATIVES
Up to this point, we have been concerned largely with building a bioeconomic model that considers all important variables. The model is based upon the fact that open access to the American lobster fishery is permitted. However, all States restrict gear to pots and traps. Each State (Maine, Massachusetts, New Hampshire, and Rhode Island) has a minimum length re- quirement; permitted minimum lengths vary from S'/h to S-'/ie inches. We are taking the array of existing regulations as given. We shall consider the economic impact of five alternative policies that could be adopted to manage or to limit entry to the entire American lobster fish- ery. These management strategies assume that some central authority such as a regional com- mission could impose these regulations. •'! The specific objectives of these management strate- gies will be discussed below. All strategies have two objectives in common which are (1) to protect the resource from overex])loitation and (2) to allow maximum freedom for operators to function in a free enterprise fashion. Further, the following strategies are meant to be illustra- tive and do not exhaust all possible alternatives. Also, two other management strategies sug- gested by Reeves (1969) and Sinclair (1960) will
30 This is subject to two qualifications. First, since we are plotting only equilibrium relationships, extinction is a possible dynamic outcome (as was mentioned previously). Second, we have implicitly assumed that in the case of American lobster, the rate of technological advance is minimal. This is a fairly realistic assumption for the in- shore trap fishery. However, in general. / = r(i), with ^'>0.
31 With the steady-state assumption, the management policies would in fact maximize the present value of the stream of net benefits over time.
be reviewed. As other management strategies are suggested both inside and outside govern- ment, the model formulated above may be used to predict their impact.
Some Possible Alternative Management Strategies for Inshore American Lobsters
1. Freeze on existing (1969) fishing effort by placing a lice)ise fee on traps: Under this scheme, the regulatory authority would calcu- late a license fee on traps which would keep the level of fishing effort constant despite an increase in the demand for lob.sters.-'- A license fee could not be levied on the individual vessel because this would not control the number of traps fished per vessel. The increased cost of operations due to the license fee would make it uneconomical for vessels to enter the fishery even though ex-vessel prices have increased. In essence, the license fee would siphon off increased revenue (or profits) from an increase in ex-vessel prices assuming the latter increases faster than cost of operations. For purposes of illustration, let us assume that we desire to manage the inshore American lobster fishery commencing in 1974. Given the estimated trend in important variables in the fishery (i.e., n, I, Qq, Y, N, CPI) to the year 1974, it would be necessary to place an estimated annual license
32 The model can derive the "correct tax" (or license fee) in a number of ways. Suppose, the regulatory author- ity wishes to freeze effort at some specified level K^. We can derive the equilibrium yield consistent with K'\ call it (A^.v)", from the yield-effort relationship. The total tax and the tax per vessel are then respectively given by:
7'^. -(a-/i(/..Y)0)(A-.v)0-AOf
K
In similar fashion, if the regulatory authority wishes to freeze effort at a level consistent with maximum sustain- able yield, we can obtain the tax that will insure this level of exploitation.
The only other taxing scheme that requires further ex- planation is a tax that will insure marginal cost pricing. Long-run industry marginal cost can be defined as:
ff/ J^\ where
dK.\
is the first derivative of (16). Total
industry cost can then be redefined as,
ydKx/bK/
This expression can be substituted into the total revenue function and solution for K, Kx can be found by iteration. The tax consistent with these solutions can then be derived by using the formulas given above, i.e., Tx, TxIK.
21
FISHERY BULLETIN VOL. 72, NO. 1
fee of $3.34 (in 1972 dollars) on each lobster trap fished. This is shown in Table 2. The reg- ulatory authority would collect over $3.5 mil- lion in license fee revenue which could be used to finance resource research, enforcement, and surveillance. It should be emi)hasized that these calculations are merely rough estimates and only serve to give the reader some idea of the magnitude of such license fee. The illustra- tive license fee is also based upon an extra- polation of trends 5 yr ahead of 1969. If we did nothing, it is estimated that the catch would be lower and more fishermen and traps would be employed in the fishery by 1974. Obviously, the situation would worsen as demand for lob- sters expanded and the fishery became increas- ingly overfished. The license fee plan does have many disadvantages. First, a license fee on traps fished does not really get at the utilization rate. One might expect that a license fee on an individual trap might induce fishermen to fish each trap more intensively and thereby reduce their number of traps. At this point, we do not have any information on utilization rates whereby the tax could be adjusted upward if utilization increased. Second, enforcement and surveillance might be difficult along the coast- line from Maine to North Carolina. Third,
and most important, the quantitative tools and projected figures needed to calculate a license fee are at best crude and would have to be used for calculations each year.
2. Reduce the existing level of fishing effort to that necessary to liarvest MSY by placing a Hcoise fee on traps: With this scheme, the regulatory authority would calculate a license fee on traps which would reduce the level of existing effort to that necessary to harvest maxi- mum sustainable yield (i.e., estimated to be about 1,011,910 traps) despite an increase in demand for lobsters.-''^ Because we are actually reducing fishing effort as opposed to freezing it at the 1969 level, the estimated 1974 license fee per trap must be higher or $5.58 (in 1972 dollars). Actual catch will not be significantly higher. The regulatory authority would receive approximately $5.6 million in license fee reven- nue. However, this plan has the same disadvan- tages of a general license fee plan indicated under alternative one.
3. Reduce the existi)ig level of fishing effort to that )iecessarjj to make the marginal cost of
33 The fishing effort needed to harvest MSY was ob- tained from equation (23) with the 1950-69 average water temperature.
Table 2. — The impact of various management schemes imposed on the inshore American lobster fishery in 1974.
|
Impact |
after the imposition |
of selected mane |
igement strategies for |
1974 |
||
|
(1) |
(2) |
(3) |
(4) |
(5) |
||
|
Estimated |
Issue "stock |
|||||
|
values before |
Freeze at |
Reduce |
Reduce |
certificate" |
||
|
Economic |
imposition of |
1969 level |
fishing |
fishing |
to vessel |
Do |
|
variables |
management |
of fishing |
effort |
effort |
owner while |
nothing |
|
strategies |
effort |
to £max |
%o MC = P |
freezing effort |
||
|
( 1 969) |
at 1969 level |
|||||
|
Catch (million lb) |
28.6 |
28.6 |
28.7 |
23.9 |
28.6 |
28.1 |
|
Value of catch |
28.0 |
36.8 |
36.9 |
31.9 |
36.8 |
36.4 |
|
(million $) |
||||||
|
Vessels (full-time |
1,900 |
1,900 |
1,798 |
1,060 |
1,900 |
2,070 |
|
equivalent) |
||||||
|
Traps (million) |
1.069 |
1.069 |
1.011 |
0.597 |
1.069 |
1.165 |
|
Ex -vessel price |
0,98 |
1.29 |
1.29 |
1.33 |
1.29 |
1.30 |
|
Total license fees |
0 |
3.56 |
5.58 |
13.3 |
0 |
0 |
|
collected (million $) |
||||||
|
License fee/vessel ($)'- |
0 |
1,877 |
3,119 |
12,622 |
0 |
0 |
|
License fee /trap ($) |
0 |
3.34 |
5.54 |
22.43 |
0 |
0 |
|
Return per vessel |
6,365 |
8,400 |
8,400 |
8,400 |
10,278 |
8,400 |
|
and fisherman |
' Projection of 1974 impact of selected management strategies. Assumes that F° = 48°; Y = $677.9 billion, (1969 prices); POP = 212.4 million; Qo + / = 183.6 million pounds and fi = $15,292. All prices and dollar values projected for 1974 ore expressed in 1972 dollars.
^ The license fee per vessel was obtained by multiplying the tax per trap by the average number of traps (562.8) fished per full-time vessel.
22
FULLENBAUM and BELL; AMERICAN LOBSTER FISHERY
knidiiigs equal to ex-ves.sel price by placitig a license fee on traps: The idea hei'e is to obtain the greatest "net economic benefit" and has been suggested by such economists as Crutch- field and Pontecorvo (1969).''^ If a regulatory authority were to try this for 1974, it would have a drastic impact on the fishery as the number of full-time equivalent vessels and traps would be reduced by approximately 47%. To accomplish this objective an estimated 1974 license fee of $22.43 (in 1972 dollars) per trap would be needed. This would yield the regulatory author- ity appro.ximately $13.3 million in revenue. From an economic point of view, it is argued that this management strategy will result in the most efficient operation of the fishery if fisher- men and vessels can easily move to other fish- eries or industries. However, this strategy may be particularly unwise in rural areas such as Maine where labor mobility is low. A drastic cutback in the number of fishermen may create social problems where the cost would greatly exceed any benefits derived from this manage- ment strategy. Therefore this management strategy is difficult, if not impossible, to justify on economic grounds for many rural areas where the fishing industry is located and also has the same disadvantages of a general license fee plan on traps as discussed above.
4. Issue "stock certificates" to each vessel ou'iier based upon average catcJt over last 5 ijr while freezing the existi)ig level of fishing effort: Under this scheme, the historic rights of each fishing firm would be recognized. In a similar manner to a private land grant procedure, the regulatory authority would simply grant each fisherman a "private" share of an existing resource or catch. The stock certificate would be evidence of private ownership. Individual fishermen would be free to catch up to their allotted share through the use of pots or other biologically permissible technology or, if they desired, trade their stock certificates to others for cash. Suppose the regulatory authority were to freeze the level of fishing effort at the 1969 level and distribute the estimated catch via a stock certificate to the existing fishermen. It should be pointed out that the regulatory author-
s'* When price is constant, maximization of net economic benefit becomes identical to the goal of maximization of rent to the fishery. This, however, is not the case when the normally downward sloping demand curve is specified.
ity fixes effort when it selects a given catch. The selected catch could be either MSY or any other level of catch deemed by the regulatory author- ity not injurious to the viability of the .stock. The expansion in demand for lobsters by 1974 would generate excess profits for those individual fish- ermen who were initially endowed with the property right. By 1974, it is estimated that a full-time lobsterman would be earning $10,278 (in 1972 dollars) a year of which $1,878 would be excess profits (i.e., above opportunity cost). If iirofits become excessive a license fee would be levied on the fishermen holding stock certif- icates to insure against increased abnormal returns and provide the regulatory authority with funding to conduct scientific investigations and enforcement. It should be noted that this plan is identical to the license fee scheme which freezes effort at its 1969 level. However, in the latter case, excess profits are taken by the regulatory authority while for this strategy, fishermen are allowed to hold onto the profits generated in the fishery. Since many fisheries are located in rural areas where earnings are traditionally low, this strategy might be justified on the basis that it will raise income levels and thereby help improve living standards to com- parable levels to those received in urban areas. This management strategy would, of course, be popular with those already in the fishery. How- ever, new entrants would have to buy .stock certificates from those initially in the fishery. This would bring up certain questions of equity and legal precedent which are beyond the scope of this article.
5. No manage Die nt strategy: When consider- ing the economic consequences of alternative management strategies (1-4), it is aJways wise to assess the results of doing nothing. This gives policymakers a better ])erspective in evaluating the benefits from taking action. The consequence of doing nothing would be overcapitalization by 1974 with an expansion in the number of full- time equivalent fishermen and traps fished. Approximately 96,000 excess traps (i.e., above that necessary to take MSY) would be in the fishery, and the catch would fall to 28.1 million pounds.
The fishery would grow increasingly over- capitalized, and the resource would be greatly overexploited as demand increased for lobsters during the 1970"s. On economic grounds, these
23
FISHERY BULLETIN VOL. 72, NO. 1
results are hardly ac-ceptable because more fish- ermen and vessels will probably be catching less.
6. Other suggested ma)iageme)it sti'ategies: Reeves (1969) has proposed a hike in license fees to eliminate the marginal or part-time fishermen. He suggests that the present $10 yearly fee in Maine be raised $10 a year over the next 9 yr to a top of $100. In 1969, a little less than one-half of the lobster fishermen were part-time. A part-time lobster fisherman is defined as one who gains less than one-half of his aniRial income from lobstering. The first step in most suggested limited entry schemes is usually to restrict the fishery to full-time utilization of cai)ital and labor. Two problems occur with this policy. First, the part-time fish- ermen may represent the most efficient way of taking the catch. If so, the full-time fishermen may be eliminated by increased license fees. Second, license fees do not directly control fish- ing effort since fishermen may fish more tra})s. However, Reeves also goes on to argue strongly for limiting the number of traps each fisherman is allowed to set. It is not quite clear whether anyone knows the optimum number of tra])s per vessel.
Rutherford. Wilder, and Frick (1967) in their study of the Canadian inshore lobster fishery endorse the system suggested by Sinclair (1960). They state:
"An alternative management system is that suggested by Sinclair (1960) for the salmon fisheries of the Pacific Coast. This would use the licensing of fishermen to limit entry into the fishery. In the first stage, lasting about five years, licenses would be reissued at a fee but no new entries would be licensed, and it would be hoped that during the period there would take place a reduction in the labour and capital input, to take the maximum sustainable catch of salmon at a considerably lower cost. After the end of the first stage, licenses would be issued by the government under competitive bidding and only in sufficient numbers to appro.ximate the most efficient scale of effort; the more competent fishermen would be able to offer the highest bids and it would be expected that the auction would recapture for the public purse a large portion of the rent from the fisheries that would otherwise accrue to the fishing enterprises under the more efficient production condi- tions in the fishery.
"An arbitrary reduction in the number of fishermen by restriction of licenses to a specified number would entail injustice and inequity as well as grave administra- tive problems in determining who should be allowed to continue fishing. The auctioning of licenses to exploit a public property resource is justifiable in a private
enterprise system of production, particularly when the state is incurring heavy expense to administer and con- serve the resource: the recovery by the state of some part of the net economic yield by means of a tax on fisher- men (or on the catch) would recoup at least part of such public expenditures, or could be used to assist former fishermen (see strategies discussed above) for instance, by buying their redundant equipment. A tax on fishermen through the auctioning of licenses has, at least, the merit of using economic means instead of arbitrary regulations to achieve a desired economic objective — the limitation of fishing effort to increase the net economic yield from the fishery. Regulations have to be enforced, usually at considerable cost, but economic sanctions tend to be, if not impartial, at least impersonal and automatic in their operation."
Actually, this latter management scheme is similar to the taxing scheme, but uses an auction rather than a direct tax.
Conclusions
The purpose of this article is to explain the use of bioeconomic models in assessing alter- native management strategies. For this purpose the data are less than optimal. However, this does not mean that we cannot take steps in the direction of fishery management. In fact, these steps must be taken to protect the resource from destruction and to achieve a better use of vessels and fishermen. It is hoped that the following conclusions will provide a helpful framework in which to consider the merits of limited entry:
1. For the inshore American lobster resource, there is every indication that the fishery has achieved maximum sustainable yield and is fully capitalized. This has been brought about by a rapid expansion in effort (i.e.. traps fished) produced by (1) free access to the resource, (2) a rising market for lobsters of all species, and (3) a secular decline in seawater temperature.
2. We have presented the bioeconomic im- pact of alternative management strategies to both conserve the resource and use it efficiently. The choice of which strategy to pursue is in the public domain and beyond the scope of this paper. However, the economic alternatives are pointed out.
LITERATURE CITED
Bell, F. W.
1972. Technological externalities and common proper- ty resources: an empirical study of the U.S. northern lobster fishery. J. Polit. Econ. 80:148-158.
24
FULLENBAUM and BELL: AMERICAN LOBSTER FISHERY
CrUTCHFIELD, J. A,, AND G. PONTECORVO.
1969. Pacific salmon fisheries: A study of irrational conservation. Johns Hopkins Press. Baltimore. Md., 220 p.
FULLENBAUM, R. F., E. W. CaRLSON, AND F. W. BeLL.
1971. Economics of production from natural re- sources: comment. Am. Econ. Rev. 61:483-487. Graham, M.
1935. Modern theory of exploiting a fishery and application to North Sea trawling. J. Cons. 10:264- 274.
GULLAND, J. A.
1961. Fishing and the stocks of fish at Iceland. Fish Invest. Minist. Agric. Fish Food (G.B.) Ser. II, 23(4): 1-32.
LOTKA. A. J.
1956. Elements of mathematical biology. Dover Publ., N.Y., 465 p.
PeLLA, J. J., AND P. K. TOMLINSON.
1969. A generalized stock production model. [In Engl, and Span.] Inter-Am. Trop. Tuna Comm. Bull. 13:421-496. Reeves, J.
1969. The lobster industry: Its operation, financing.
and economics. Master's dissertation. Stonier Grad. Sch. Banking, Rutgers Univ., New Brunswick, N.J., 170 p. Rutherford, J. B., D. G. Wilder, and H. C. Frick.
1967. An economic appraisal of the Canadian lob- ster fishery. Fish. Res. Board Can., Bull. 157, 126 p.
SCHAEFER, M. B.
1954. Some aspects of the dynamics of populations important to the management of commercial marine fisheries. Inter-Am. Trop. Tuna Comm., Bull. 1:27-56. Sinclair, S.
1960. License limitation — British Columbia: A method of economic fisheries management. Chap- ter III, p. 98. Can. Dep. Fish. 256 p. Thomas, J. C.
1970. An analysis of the commercial lobster (Homants americanus) fishery along the coast of Maine, August 1966 through December 1970. Final Rep., Lobster Res. Prog. State Maine, Dep. Sea Shore Fish., 73 p. Worcester, D. A., Jr.
1969. Pecuniary and technological externality, factor rents, and social costs. Am. Econ. Rev. 59:873-885.
Appendix Table — Economic variables associated with the U.S. inshore American lobster fishery, 1950-69.
|
Per capita |
|||||||||||
|
disposable |
Mean annual |
||||||||||
|
Ex-vessel |
personal income |
seawater temp- |
|||||||||
|
price divided |
Per capita |
divided by |
Consumer |
erature ot |
|||||||
|
Catch |
Traps |
Catch |
Ex -vessel |
by consumer |
consumption |
consumer price |
price index |
Boothboy |
|||
|
Year |
by traps |
Value |
fished |
per trap |
price |
price index |
Year |
of lobsters |
index |
(1967= 100) |
Harbor, Maine |
|
Thousand |
Tlunisand |
Nmnher |
Pounds |
Cems per |
Cents per |
Pounds |
Dollars |
Dei^rees |
|||
|
pounds |
dollar \ |
pound |
pound |
(live weiKhrl |
Fahrenheit |
||||||
|
1950 |
22,914 |
8,283 |
578,930 |
39.6 |
36.1 |
50.1 |
1950 |
0.585 |
1,892 |
72.1 |
49.3 |
|
1951 |
25,749 |
9,328 |
512,812 |
50.2 |
36.2 |
46.6 |
1951 |
.651 |
1,888 |
77.8 |
51.4 |
|
1952 |
24,681 |
10,469 |
544,730 |
45.3 |
42.4 |
53.4 |
1952 |
.638 |
1,909 |
79.5 |
50.2 |
|
1953 |
27,509 |
10,687 |
569,081 |
48.3 |
38.8 |
48.5 |
1953 |
.710 |
1,976 |
80.1 |
52.0 |
|
1954 |
26,628 |
10,250 |
628,209 |
42.4 |
38.5 |
47.8 |
1954 |
.690 |
1,969 |
80.5 |
50.3 |
|
1955 |
27,886 |
11,003 |
669,229 |
41.7 |
39.5 |
49.2 |
1955 |
.734 |
2,077 |
80.2 |
50.0 |
|
1956 |
25,386 |
11,584 |
666,887 |
38.1 |
45.6 |
56.1 |
1956 |
.704 |
2,141 |
81.4 |
48.6 |
|
1957 |
29,358 |
11,263 |
688,815 |
42.6 |
38.4 |
45.6 |
1957 |
.806 |
2,136 |
84.3 |
48.8 |
|
1958 |
26,143 |
12,890 |
753,503 |
34.7 |
49.3 |
56.9 |
1958 |
.736 |
2,114 |
86.6 |
47.4 |
|
1959 |
27,752 |
14,043 |
856,794 |
32.4 |
50.6 |
58.0 |
1959 |
.763 |
2,182 |
87.3 |
47.0 |
|
1960 |
29,345 |
13,657 |
844,110 |
34.8 |
46.5 |
52.5 |
1960 |
.830 |
2,185 |
88.7 |
47.9 |
|
1961 |
25,621 |
13,662 |
895,098 |
28.6 |
53.3 |
59.5 |
1961 |
.810 |
2,214 |
89.6 |
47.3 |
|
1962 |
26,728 |
13,770 |
909,318 |
29.4 |
51.5 |
56.9 |
1962 |
.855 |
2,280 |
90.6 |
46.6 |
|
1963 |
27,210 |
15,299 |
866,900 |
31.4 |
56.2 |
61.3 |
1963 |
.938 |
2,333 |
91.7 |
47.9 |
|
1964 |
26,844 |
17,689 |
904,233 |
29.7 |
65.9 |
70.9 |
1964 |
.935 |
2,459 |
92.9 |
46.9 |
|
1965 |
24,737 |
18,764 |
949,045 |
26.1 |
75.9 |
80.3 |
1965 |
.884 |
2,578 |
94.5 |
45.8 |
|
1966 |
25,606 |
19,517 |
947,113 |
27.0 |
76.2 |
78.4 |
1966 |
.873 |
2,680 |
97.2 |
45.7 |
|
1967 |
22,098 |
18,162 |
907,956 |
24.3 |
82.2 |
82.2 |
1967 |
.882 |
2,751 |
100.0 |
45.1 |
|
1968 |
26,918 |
20,648 |
966,335 |
27.9 |
76.7 |
73.6 |
1968 |
.960 |
2,827 |
104.2 |
46.6 |
|
1969 |
26,930 |
22,997 |
1,061,807 |
25.4 |
85.4 |
77.8 |
1969 |
.999 |
2,851 |
109.8 |
48.0 |
|
Source |
Fishery |
Statistics ol |
the Uni |
ed States |
, various |
years, U.S. |
Department of Commerce, Bureau |
3f Labor Statistics, and |
|||
|
Robert |
Dow. |
25
DAILY ACTIVITY, MOVEMENTS, FEEDING, AND SEASONAL OCCURRENCE IN THE TAUTOG, TAUIOGA ONITIS^
BoRi L. Olla, Allen J. Bejda, and A. Dale Martin-
ABSTRACT
Observations were made on the activity and movements of adult tautog, Taiitogu oniiis, in their natural habitat using scuba and by monitoring the movements of individual fish by ultrasonic tracking. Results showed tautog to be active during the day and inactive at night. Fish larger than 30 cm moved out from the night resting place (home site) each day to feed, while younger fish (^25 cm) remained and fed in close proximity to the home site. Examination of digestive tracts from various-sized fish showed the blue mussel, Mytiliis editlis, to be the principal food for this population. While older fish appeared to move offshore for the winter, the younger fish remained inshore, wintering over in a torpid state. The significance of the tautog's differential responsiveness, food habits, and daily and seasonal movements are discussed.
The tautog, Tautoga o)iitis (L.), an inhabitant of the western Atlantic, ranges from Nova Scotia to South Carolina, being most abundant between Cape Cod and the Delaware Capes (Bigelow and Schroeder, 1953:478-484). Its distribution is limited primarily to inshore regions with individual populations being highly localized (Cooper, 1966). This fish lives in close associa- tion with rocky places, wrecks, pilings, jetties, or almost any bottom discontinuity and for part of its range, is a prominent member of inshore benthic communities. Unlike the majority of labrids, this species is valued as a game fish and is an excellent table fish.
Our aim in this work was to observe and describe the behavior of adult tautog in situ and to relate our findings to the animal's life habits and history. Our queries primarily con- cerned daily activity and movements, feeding, and seasonal occurrence. The study was carried out on a population residing in Great South Bay, N.Y., using scuba and ultrasonic tracking.
MATERIALS AND METHODS
The study area was along the south shore of Great South Bay, Long Island, N.Y., extending
' This work was supported in part by a grant from the U.S. Atomic Energy Commission, number AT(49-7)3045.
- Sandy Hook Laboratory, Middle Atlantic Coastal Fisheries Center, National Marine Fisheries Service, NOAA, Highlands, NJ 07732.
east from the Fire Island Inlet Bridge to 2 km east of the Fire Island Light (Figure 1). Water depth in the study area ranged from 2.4 to 8.8 m with the bottom composed primarily of sand, gravel, and shell.
Two methods were employed to observe the activity and movements of the fish: (1) ultra- sonic tracking of a single fish and (2) direct underwater observations while using scuba.
Twelve fish were tracked at different times from August through September 1971 and June through October 1972 (Table 1). Fish were captured at night within the Fire Island Coast Guard basin by a scuba diver using a hand-held net, and each fish was held in a floating cage for periods ranging from. 10 to 108 h before a transmitter was attached.
ATLANTIC OCEAN
tOOO METERS
Manuscript accepted June 1973.
FISHERY BULLETIN: VOL. 72. NO, 1, 1974.
Figure 1. — Study area and areas (A-H) of tautog move- ment as presented in Table 1.
27
FISHERY BULLETIN: VOL. 72, NO. 1
Table 1. — Locations and duration of stay (h) of individual tautog during their daily movements as determined by ultra- sonic tracking.
Tautog no.
Day
Night
1 TL (cm) Age'/sex
Release (dote/time) Track duration (h) Mean temperature
2 TL (cm) Age/sex
Release (date/time) Track duration (h) Mean temperature
3 TL (cm) Age/sex
Release (date/time) Track duration (h) Mean temperature
4 TL (cm) Age/sex
Release (dote/time) Track duration (h) Mean temperature
5 TL (cm) Age/sex
Release (date/time) Track duration (h) ■ Mean temperature
6 TL (cm) Age/sex
Release (date/time) Track duration (h) Mean temperature
7 TL (cm) Age/sex
Release (date/time) Track duration (h) Mean temperature
45
12/9
7-25-72/1310
67.5
19.2°C
42
10/9
8- 1 -72/0940
68.3
21.2°C
42
10/9
8-8-72/1215
66.5
20.4°C
43
916
9-15-71/0830 47.5 22.0°C
38
7/9
9-27-71/1400
41.5
18.1°C
47
11/d
8-16-71/1830 41.5 21.7°C
20
3/9
10-4-72/0930
34.0
16.8°C
A3'( 5.0)- Al( 2.2) A4( 9.8) A4( 2.6) Al(11.4) Al(lO.O) Al(14.1) A3(10.2) A4( 1.9)
Al( 0.8) A4(11.5) A3( 3.1) A4( 0.5) Al( 9.6) Al( 9.8) Al( 9.6) A4( 0.4) A5( 2.3) A4( 9.2) C ( 8.4) A5( 1.8)
Al( 3.0) A4( 0.9) A5( 6.2) A5(0.3) Al(11.3) Al(11.6) Al(10.8) A4( 3.0) A9(10.3) A9( 7.0)
Al( 1.0) A3( 2.5) A4( 0.5)
A4( 5.7) A5( 0.8)
A6( 0.6) A6( 4.5)
A7( 2.3) A7( 0.8)
Al( 0.3) A5( 2.7) A5( 1.0)
A4( 0.2) A6( 1.4)
A7( 4.0)
A8( 0.1)
Al( 1.4) A2(10.9) F ( 4.1)
A5( 0,3)
Al( 9.4) Al(12.5)
Al(12,8) Al(15.6)
Al(16.6) Al(15.1)
Al(10.3) G (12.2)
Al(11.5) Al( 0.6)
The transmitter emitted pulsed signals at 70 kHz (kilohertz). Those used for small fish (20- 25 cm) measured 30 x 9 mm (manufactured by Chipman Instruments''). Larger transmitters, 65 X 14 mm (SR-69B, Smith-Root Inc.) were used for the remaining fish (38-50 cm).
The pharyngeal mill apparatus of the fish precluded internal insertion of the transmitter. This necessitated external attachment through the dorsal musculature, with nylon monofila- ment line just below the midpoint of the dorsal fin. On each side of the body, rubber disks (25- mm diameter) were used to prevent the flesh from tearing. Tags were made neutrally buoy- ant by the addition of a styrofoam collar coated with silicone sealant. Following attachment of the transmitter, fish were held in a 50-liter
•' Reference to trade names in this publication docs not imply endorsement of commercial products by the Na- tional Marine Fisheries Service.
tank for 15 to 30 min to insure that the fish were responsive and that the transmitter was operating normally.
Fish were released within the basin and tracked from a 5.2-m skiff. The signal was moni- tored with hydrophone and sonic receiver (Model SR-70-H and TA-60 respectively, Smith- Root Inc.) in a manner similar to that described by McCleave and Horrall (1970).
The location of each fish was recorded in relation to local landmarks. We considered a fish active whenever a change in transmitter signal was detected. Direct underwater obser- vations confirmed that we were able to detect abrui)t changes in the fish's orientation and straight line movement over 1 m. The data were subse(iuently condensed to indicate the i)res- ence of a fish for a i)eriod of time at a specific location (Table 1).
For each track, we recorded current velocity,
28
OLLA, BEJDA, and MARTIN: ACTIVITY OF TAVTOGA ONITIS
Table 1. — Locations and diiralit)n of stay (h) of individual tautog during their daily movements as determined by ultra- sonic tracking, continued.
|
Tautog |
Uay |
|||
|
no. |
1 |
2 |
3 4 |
|
|
8 TL (cm) |
25 |
Al( 7.7) |
Al(12.5) |
Al(12.5) Al( 0.6) |
|
Age/sex |
4/9 |
|||
|
Release (date/time) |
10-3-72/1 115 |
|||
|
Track duration (h) |
67.7 |
|||
|
Mean temperature |
16.8°C |
|||
|
9 TL (cm) |
50 |
D ( 0.5) |
D (10.1) |
D ( 4.9) |
|
Age/sex |
14/(5 |
E (10.9) |
E ( 3.0) |
|
|
Release (date/time) |
6-14-72/0855 |
F ( 0.6) |
||
|
Track duration (h) |
48.8 |
|||
|
Mean temperature |
14.1°C |
|||
|
Renewed track |
D { 3.9) |
D (16.8) |
D (10.2) |
|
|
Dote/time |
6-19-72/1750 |
E ( 3.1) |
||
|
Trock duration (h) |
49.9 |
|||
|
Mean temperature |
15.5°C |
|||
|
10 TL (cm) |
43 |
A5( 8.6) |
A5( 9.8) |
|
|
Age/sex |
9/c5 |
A6( 5.6) |
||
|
Release (date/time) |
6-27-72/1025 |
|||
|
Track duration (h) |
42.5 |
|||
|
Mean tempera'ure |
17.3°C |
|||
|
n TL (cm) |
44 |
Al( 1.1) |
||
|
Age/sex |
11/9 |
A2( 1.8) |
||
|
Release (date/time) |
6-5-72/1345 |
B ( 0.6) |
||
|
Track duration (h) |
3.5 |
|||
|
Mean temperature |
13.4°C |
|||
|
12 TL (cm) |
45 |
Al( 0.3) |
||
|
Age/sex |
12/9 |
A5( 3.2) |
||
|
Release (date/time) |
6-12-72/1145 |
A6( 2.7) |
||
|
Track duration (h) |
8.3 |
A8( 0.3) |
||
|
Mean temperature |
13.8°C |
B ( 1.1) C ( 0.7) |
Night
G ( 8.0) D ( 7.9)
D ( 7.9) D ( 7.9)
A5(10.2) A5( 8.3)
' Location as presented in Figures 1 and 2.
- Hours given in parentheses.
^ Age estimated from calculated total lengths by Cooper ( 1967) .
stage of tide, cloud cover, water temperature, and water transparency. Current velocity was measured either with a Beauvert midget cur- rent meter or by the float method. The current velocity ranged from 0.65 to 1.75 m/s. Temper- ature was measured with a thermistor and transparency with a secchi disk. Cloud cover was visually estimated.
In conjunction with our tracking, we directly observed tautog in the study area with scuba for a total of 135 h (90 h daytime and 45 h nighttime).
To identify periods of feeding as well as the types and amounts of food ingested, we ex- amined the digestive tracts of fish collected at different times of the day and night. We mea- sured the relative dige.stive tract fullness of each volumetrically with the fullness index being the quotient of displacement volume of empty tract/displacement volume of tract with con- tents.
Determination of the maximum size of mussel
that the tautog could ingest and of the maximum size it could crush was made by inserting dif- ferent size mussels into the mouth and into the anterior opening of the pharyngeal mill. The maximum ingestable size was defined as the largest mussel that could be completely enclosed in the mouth. The maximum crushable size was the largest mussel that could be partially grasped by the pharyngeal teeth.
To aid in describing the method of feeding on mussels, at infrequent intervals over a 16-mo period, we directly observed and used cine anal- ysis of three individuals 25 to 38 cm, held in a 2,200-liter aquarium.
RESULTS
Activity and Movements
The fish which we tracked were active during the day and inactive at night. There was some
29
FISHERY BULLETIN: VOL. 72. NO. 1
degree of variation in tlie precise time that activ- ity began or ceased relative to morning and evening civil twilight (Table 2). Activity began from 10 min before to 69 min after the start of morning twilight. Cessation of activity, however, was more variable, ranging from 222 min before to 69 min after the end of evening twilight. Al- though we were unable to arrive at the cause for this variation, there were indications that cloud cover and water transparency, both affecting light penetration, might play a role. Our direct scuba observations (135 h of observation) on untagged tautog showed that the fish were active during the day and inactive at night. Activity as well as responsiveness at night were at such a low level that we were able to touch individual fish or catch them easily with a hand-held net. Five fish (No. 1-5, Table 1), tracked at dif- ferent times from July through September 1971 and 1972, exhibited similar j^atterns in their daily movements. Each morning at the onset of activity or soon after, the fish moved out and usually remained within 500 m of the basin. They spent most of each day at locations in
which there were large concentrations of blue mussel {Mijfihis cdnlis) (areas A2-A9, Figure 2; Table 1). Towards late afternoon or early evening, the fish returned to the basin and with- in 1 to 198 min (x= 55.7), settled in one location and remained throughout the night in an inac- tive state.
Another fish (No. 6, Table 1) tracked during this period returned to the basin the first night after being released, following the same i)attern as fishes 1 to 5. However, after s})ending most of the second day in close proximity to the basin, it did not return but rather, at 172 min prior to the end of evening twilight, swam 6.2 km in a direct easterly course to an artificial reef (consisting of sunken barges and tires) where it si)ent the night (area G, Figure 1).
Underwater observations made during July through mid-October showed that the number of fish, measuring about 30 to 50 cm, in close prox- imity to the basin increased just prior to and immediately after the beginning of evening twilight in comparison to the number that were present during the day. Comparing these obser-
Table 2. — Onset and end of the daily activity of individual tautog relative to morning and evening
civil twilight (MCT and ECT').
|
Mean time and |
range (min) to |
|||
|
Onset |
of activity |
End of activity |
||
|
Tautog no. |
Prior to MCT |
Following MCT |
Prior to ECT |
Following ECT |
|
1 |
27.0 (21.0 to 35.0) |
122.0 (43.0 to 222.0) |
||
|
2 |
20.0 (t0.0to30.0) |
14.7 ( 8.0 to 26.0) |
||
|
3 |
26.0 (12.0 to 43.0) |
71.0 (39.0 to 116.0) |
||
|
4 |
7.0 (4.0 to 10.0) |
78.5 (72.0 to 85.0) |
||
|
5 |
23.0 (18.0 to 28.0) |
47.5 (12.0 to 83.0) |
||
|
6 |
54.5 (52.0 to 57.0) |
28.0 ( 4.0 to 52.0) |
||
|
7 |
35.0 |
68.0 (54.0 to 82.0) |
||
|
8 |
27.0 (13.0 to 45.0) |
75.3 (51.0 to 88.0) |
||
|
9 |
62.0 (49.0 to 69.0) |
131.0 (26.0 to 158.0) |
69.0 |
|
|
10 |
14.0 |
51.0 (28.0 to 74.0) |
' MCT: start of morning civil twilight. ECT: end of evening civil twilight.
30
OLLA, BEJDA, and.MARTIN: ACTIVITY OF TAUTOGA ONITIS
100 METERS
N
/
Figure 2. — Areas demarcating the locations of tautog during their daily movements as presented in Table 1 (an enlargement of area A, Figure 1).
vations with our tracks of similar-sized fish, we were led to conclude that this increase was the result of the normal nightly return to the basin. However the number of smaller fish (^25 cm) appeared to remain the same throughout the day and during evening twilight, i.e., there was no discernible increase at evening twilight. To affirm whether the smaller, younger fish did in fact remain closer to the basin during the day than the larger, older ones, we tagged two fish 20 and 25 cm (No. 7 and 8, Table 1), tracking one for 34 and the other for 66.8 h. These fish exhibited the typical habit of the larger fish of being active during the day and inactive at night (Table 2). However, in contrast to the larger fish, these smaller fish remained within the basin and never ventured farther than 2 m from the walls. Examination of the digestive tract of one of these smaller fish, recaptured after track- ing had been terminated, showed the presence of mussels throughout the tract, indicating that this fish had been feeding on mussels at- tached to the basin walls or other substrate within the basin.
These data indicate that tautog occur as an essentially localized population at least from July through mid-October. The basin acts as a focal point for the population, providing a suit- able night habitat for all fish and a forage area for smaller fish.
Four fish (No. 9-12, Table 1) tracked during June 1972 exhibited quite different patterns of daily movements. Two of these (No. 9 and 10) ranged farther during the day and spent the night at various locations other than the basin. Tracking was discontinued on the other two fish of this group (No. 11 and 12) during the first day due to inclement weather. However, a search the night following tracking termina- tion and on three successive nights failed to detect the presence of either fish in or around the basin. They, too, evidently spent the night at other locations.
The major difference in fish tracked during June from all other fish tracked was that all June fish were in spawning condition, readily extruding sperm or ova during the tagging pro- cedure. Further, if this population bears any similarities to the Narragansett Bay popula- tion (Cooper, 1966), we surmise that during June, fish are still arriving inshore from their offshore wintering area and have not yet be- come localized (at least fish of the size we were tracking).
On 26 September 1972, during the day, we sighted just outside the basin (Area 3, Figure 2) a tautog with a transmitter attached. Although we could not ascertain when this fish was tagged, it had been 49 days since the last tagging. The fish, which appeared normally responsive, had either remained localized within this area for at least 49 days or possibly was one of the four fish tagged during June that had not returned to the basin at that time.
Feeding
There were varying amounts of food through- out the digestive tracts of fish sampled at vari- ous times of the day and just after evening twi- light (Table 3). The tracts of fish sampled just prior to morning twilight (23-83 min), while still in an inactive night condition, were empty. Thus it appears that the fish feed throughout the day, beginning soon after morning twilight and continuing up to evening twilight. Assum- ing that the fish sampled just before morning
31
twilight had fed up to the previous evening twilight, passage through the digestive tract while the animals were quiescent took 8 h or less.
Examination of the matter ingested showed that 70% of the fish sampled contained 78.4 to 100% mussels, by volume, in various stages of digestion (Table 3). Next in abundance were remains of various decapod and cirriped crus- taceans, followed by an assortment of other in- vertebrates and debris (vegetable matter, sand, and gravel), with some of the latter probably being ingested incidentally with the mussels. All but two of the fish examined contained over 50% mussels, by volume, indicating that mus- sels are the principal food for this population.
Observations on the tautog's method of feed- ing on mussels, in both the field and laboratory, revealed that after approaching a clump of mussels, the fish would grasp one or several at a time with the anterior canine teeth and then tear them from the substrate with an intense lateral or shaking movement of the head. In no case, in either the field or laboratory, did the initial ingestion process involve crushing with
FISHERY BULLETIN: VOL 11. NO. 1
the canines. After initial ingestion, muscular contractions in the bucco-pharyngeal area were clearly seen, evidentally resulting from the shells being crushed by the pharyngeal teeth. When a clump of mussels attached by byssal threads was too large to be processed by the pharyngeal teeth, the fish would alternately ingest and egest the clump until it was sepa- rated into a smaller crushable size.
The mussels in the digestive tracts consisted primarily of specimens averaging 11.9 mm in length and estimated to be 1 to 2 yr old (Table 3). There was an obvious selection of young, small mussels by all-sized fish.
While factors such as ease of crushing and a greater digestive efficiency may be involved in the tautog's preference for small, young mus- sels, we found another possible cause related to the limitations imposed by the dimensions of the pharyngeal area where the mussels are crushed. The mouth can accommodate much larger mussels than the crushing apparatus is able to process. For example in the laboratory on 20 occasions, we saw fish that were starved for more than a day attempting to eat mussels
Table 3. — Relative fullness and contents of tautog digestive tracts.
|
°o of total gut content! |
Median |
||||||
|
% of |
|||||||
|
Time of |
Fish |
Decapod |
length of |
mussels |
|||
|
capture |
length |
Fullness |
and cirriped |
mussels |
less than |
||
|
(EDT) |
(cm) |
index ' |
Mussels |
crustaceans |
Other |
(mm) |
30 mm |
|
0400-0500 . |
23.5 23.5 45.0 37.0 46.0 |
1.0 1.0 1.0 1.0 1.0 |
|||||
|
0800-0830 |
24.0 |
0.8 |
85.7 |
5.8 |
8.5 |
14 |
100.0 |
|
27.5 |
0.7 |
100.0 |
12 |
100.0 |
|||
|
26.5 |
0.7 |
99.5 |
0.5 |
14 |
100.0 |
||
|
34.0 |
0.8 |
62.5 |
37.5 |
16 |
100.0 |
||
|
1200-1300 |
31.0 |
0.6 |
89.6 |
4.5 |
5.9 |
15 |
100.0 |
|
36.5 |
0.5 |
65.3 |
27.0 |
7.7 |
8 |
100.0 |
|
|
37.5 |
0.6 |
78.5 |
16.1 |
5.4 |
16 |
100.0 |
|
|
21.0 |
0.7 |
98.6 |
1.4 |
11 |
100.0 |
||
|
24.5 |
0.7 |
100.0 |
5 |
100.0 |
|||
|
32.0 |
0.4 |
95.2 |
4.8 |
15 |
100.0 |
||
|
29.0 |
0.4 |
54.5 |
36.4 |
9.1 |
10 |
100.0 |
|
|
1600-1700 |
40.0 |
0.7 |
99.1 |
0.6 |
0.3 |
8 |
100.0 |
|
32.0 |
0.4 |
92.2 |
6.0 |
1.8 |
8 |
100.0 |
|
|
32.5 |
0.6 |
31.3 |
68.1 |
0.6 |
8 |
100.0 |
|
|
1930-2000 |
44.0 |
0.4 |
90.4 |
9.6 |
14 |
88.1 |
|
|
36.0 |
0.6 |
45.9 |
41.3 |
12.8 |
12 |
87.5 |
|
|
46.0 |
0.6 |
65.7 |
32.9 |
1.4 |
10 |
53.8 |
|
|
37.0 |
0.6 |
92.3 |
7.7 |
15 |
100.0 |
||
|
42.5 |
0.4 |
94.0 |
6.0 |
16 |
72.7 |
||
|
-20.0 |
0.6 |
78.4 |
21.6 |
11 |
100.0 |
' Fullness index — volume empty tract/volume of tract with contents. - Fish no. 7 (Table 1) captured at end of track.
32
OLLA. BEJDA, and MARTIN: ACTIVITY OF TAUTOGA ONITIS
larger than could be crushed by the pharyngeal teeth. The fish would ingest the mussel, unsuc- cessfully attempt to crush it, and then egest it, the process being repeated 20 to 30 times. We also found in a preliminary determination of the maximum crushable size that fish, 34 to 53 cm, could crush mussels that were only 0.47 times the maximum size they could ingest.
Seasonal Movements
Direct observations made during the day with scuba from October 1971 through May 1972 and from October 1972 through January 1973 indicated that there was a difference in the seasonal movement between small fish (^25 cm, 2-3 yr old) and large fish (>25 cm, >4 yr old). The ages of fish were estimated from calculated total lengths by Cooper (1967). Tautog of vary- ing sizes were observed in close proximity to the basin on 12 October 1971, at an average water temperature of 17.0°C (range: 15.2°- 19.5 °C). On 1 November with the water temper- ature averaging 10.0°C (range: 8.9°-10.6°C), no large tautog were sighted, but about 25 small ones were seen swimming within 1 m of the basin walls. Small fish were still active on 18 November (water temperature 10.0° C: 9.7°-10.1°C). On 9 December 1971, and 5 January 1972, with temperatures ranging from 4.0° to 5.5°C, a total of approximately 40 small tautog was sighted within the basin. These fish appeared lethargic and rested against the basin walls. When prodded by a diver, they moved only a few feet before settling to the bottom once again.
Both large and small fish were sighted on 10 May 1972 with an average temperature of 10.6°C (range: 8.5°-11.5°C) and appeared nor- mally active.
Diving observations the following fall and winter substantially supported the fact that small fish wintered inshore. On 2 October 1972, we sighted normally active large and small tautog (water temperature 16.8°C: 16.2°- 17.7° C). On 26 October with the temperature averaging 10.0°C (range: 9.6°-10.5°C), we found no large fish but sighted at least 30 small fish which appeared normally active. During dives on 27 November and 29 December 1972, and 9 January 1973, with the temperature rang- ing 2.0° to 4.8°C, we sighted approximately 35 small fish (^ 25 cm) lying in a torpid state on
the bottom between pilings and the basin walls or in bottom depressions within 10 cm of the wall. Some of these fish were partially covered with silt. Opercular movements were so shallow as to be almost undiscernible. Examination of the digestive tracts of five fish captured during this period showed that the fish had not eaten for some time as indicated by the empty and flaccid condition of the tracts.
We concluded from these observations that fish at least larger than 25 cm moved offshore to winter, agreeing with the conclusions of Cooper (1966) for a population residing in Nar- ragansett Bay, Rhode Island. However, small fish (approximately ^25 cm) remained inshore throughout the year in close proximity to the home site.
DISCUSSION
The tautog's pattern of being active during the day and inactive at night is a typical labrid trait having been observed in a number of spe- cies. For example, field observations in the Pa- cific by Hobson (1965, 1968, 1972) showed this pattern to be present in five species (Bodiaiius diplotaeiiia, Halichoeres )iicholsi, Labroides phthirophagus, Thalassoma duperrey, and T. lucasanum). Th* pattern was presumed to be present in Hali^oeres dispilus, Hemipteronotus mundiceps, and H. pavoninus since the fish were observed in the active state during the day but not sighted at night, having apparently buried under sand or rested in crevices. Field obser- vations in the Atlantic by'^arck and Davis (1966) on Bodianus rufus, Clepticus parrai, Lachitolaimus ma.vimus, and Thalassoma bi- fasciatum also show the typical labrid day ac- tive/night inactive pattern.
Whether a labrid species spends the night buried under sand or lying in cracks or crevices, all appear to be in a state of low responsiveness. Tauber and Weitzman (1969) investigated the level of responsiveness of the slippery dick, Irideo bivittata, at night. They found the fish to be in a state that resembled the mammalian sleep phase characterized by decreased respon- siveness to altering stimuli, diminished or ir- regular respiration, and eye movement activity.
The low level of responsiveness present at night in labrids and other species with a similar habit has wide ramifications with regard to
33
FISHERY BULLETIN: VOL. 72. NO. 1
susceptibility to environmental stress. The prob- ability that fish would be able to respond and escape potentially lethal environmental pertur- bations during the inactive night phase would be less than if the same stress were applied dur- ing the day. Physiological responses would also differ. Differential susceptibility to stresses as related to the daily rhythm has been clearly established (for discussion and review, see Reinberg. 1967).
During most of the summer and into early fall, fish of the colony we studied had a fairly well defined home range (Gerking, 1959) with the basin acting as a focal point or home site, providing a suitable night habitat for all-sized fish. While larger fish (^30 cm) moved out each day to feed, the smaller fish (^25 cm) foraged along or in close proximity to the basin walls. The adaptation of young fish re- maining close to the home site may relate to effectively protecting them against predators. On one occasion while diving in early July 1972, we observed three striped bass {Moroue .sa.r- atilis, 80-90 cm) actively pursuing and attempt- ing to capture young tautog (^25 cm) from a group of 30 to 40. The tautog were within 1 m of the basin wall at the onset of the attack. They escaped from the predators by swimming directly to the wall where they remained in crevices. The older fish, not as susceptible to predation, moves out to feed, resulting in a fuller utilization of the potential energy re- sources of the area and in the probable reduc- tion of feeding competition among individuals. The reduction in the probability of feeding com- petition seemed especially critical since all sizes studied preferred, to a large extent, simi- lar-sized mussels. This daily movement of the larger fish out of the basin also seemed to make the home site a nursery for young fish.
Our obsen^ations that tautog larger than 30 cm (approximately 5 yr or older) were not present in the vicinity of the basin after the end of October circumstantially agree with the finding of Cooper (1966) that Narragansett Bay fish of similar size wintered offshore. In contrast, our results showed that younger fish remained inshore throughout the year, winter- ing at the home site in a torpid, nonfeeding state. It is apparent that the younger fish are highly dependent on the home site throughout the year for at least the first 3 to 4 and perhaps 5 yr of their life. The habit of remaining inshore
over. the winter is not unknown in labrids. Green and Farwell (1971) found various-sized cunner, Tautogolabrus adspersus, lying in a torpid state inshore when temperatures fell below 5°C.
Although tautog feed readily on other types of food, the most abundant food available and found most frequently in the digestive tract was mussels. Mussels were predominantly less than 30 mm long, indicating an average age of 1 to 2 yr (Savage, 1956). The next most abun- dant food found in the digestive tract was vari- ous crustaceans, with only negligible amounts of other items. It seemed that, on the basis of our diving observations, the crustacean popula- tion, in terms of a potential alternate food source for the tautog in this area, did not ap- proach the abundance of mussels in the 1 to 2 yr class. We surmise that the equilibrium of the population, in terms of food resources, is highly dependent on a single food item, with no alter- nate potentially serving as a sustaining element.
Environmental perturbations that would directly affect 1- to 2-yr-old mussels or any of the pre-adult stages, would lead to a high prob- ability of stress in the tautog population. This would be especially true for young fish (3 yr or less) since they seem especially dependent upon the home site. This dependence on the home site raises the question of whether or not it is within their capability to move out and seek new feeding areas and if so, how successful would they be.
Another obvious limiting element of the population is a suitable physical structure which all-sized tautog require during their night inactive phase and upon which young tautog seem totally dependent. In areas where food resources are in relative abundance to support a population, the introduction of a suitable physical habitat could lead to the es- tablishment of new discrete colonies.
ACKNOWLEDGMENTS
We wish to thank the U.S. Coast Guard, Fire Island, New York, and Charles Entenmann for their assistance and cooperation. Our apprecia- tion is extended to James Johnson, National Marine Fisheries Service, and Case Groot, Fisheries Research Board of Canada, for their advice and encouragement concerning the ultra- sonic tracking portion of the study. In addition,
34
OLLA, BEJDA. and MARTIN: ACTIVITY OF TAUTOGA OMTIS
we wish to thank Ralph Sheprow for his tech- nical assistance during the study.
LITERATURE CITED
BiGELOW, H. B.. AND W. C. SCHROEDER.
1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv., Fish. Bull. 53, 577 p. Cooper, R. A.
1966. Migration and population estimation of the tautog, Taiitoga onitis (Linnaeus), from Rhode Island. Trans. Am. Fish. Soc. 95:239-247.
1967. Age and growth of the tautog. Tautoga onitis (Linnaeus), from Rhode Island. Trans. Am. Fish. Soc. 96: 134-142.
Gerking, S. D.
1959. The restricted movement of fish populations. Biol. Rev. (Camb.) 34:221-242. Green, J. M., and M. Farwell.
1971. Winter habits of the cunner, Taiitogolabrus adspersus (Walbaum 1792), in Newfoundland. Can. J. Zool.49:1497-1499. HOBSON, E. S.
1965. Diurnal-nocturnal activity of some inshore
fishes in the Gulf of California. Copeia 1965:291- 302.
1968. Predatory behavior of some shore fishes in the Gulf of California. U.S. Fish Wildl. Serv., Res. Rep. 73, 92 p.
1972. Activity of Hawaiian reef fishes during the evening and morning transitions between daylight and darkness. Fish. Bull., U.S. 70:715-740. McCleave, J. D., AND R. M. Horrall.
1970. Ultrasonic tracking of homing cutthroat trout (Salmo clarki) in Yellowstone Lake. J. Fish. Res. Board Can. 27:715-730. Reinberg, a.
1967. The hours of changing responsiveness or sus- ceptibility. Perspect. Biol. Med. 11:111-128. Savage, R. E.
1956. The great spatfall of mussels (Mytilus edulis L.) in the River Conway estuary in spring 1940. G. B. Minist. Agric. Fish. Food., Fish. Invest. Ser. II. 20(7): 1-22. Starck, W. a., II, AND W. p. Davis.
1966. Night habits of fishes of Alligator Reef, Florida. Ichthyol. Aquarium J. 38:3 13-356. Tauber, E. S., AND E. D. Weitzman.
1969. Eye movements during behavioral inactivity in certain Bermuda reef fish. Commun. Behav. Biol. Part A 3:131-135.
35
AN EXAMINATION OF THE YIELD PER RECRUIT
BASIS FOR A MINIMUM SIZE REGULATION FOR
ATLANTIC YELLOWFIN TUNA, IHUNNUS ALBACARES
W. H. Lenarz. W. W. Fox, Jr., G. T. Sakagawa, AND B. J. Rothschild'
ABSTRACT
Some of the conceptual foundations of yield-per-recruit analysis as a management tool and as applied to the Atlantic yellowfin tuna fishery were critically explored. Problems examined include: (1) estimating the current state of the fishery in terms of a knife-edged recruitment approximation, (2) inferring consequences of management action from the yield-per-recruit isopleth, (3) the difficulty in achieving a maximum yield per recruit when there exist several gear types exploiting different size ranges, (4) the difficulty in obtaining projected increases in yield per recruit when the killing and discarding (dumping) of fish smaller than the optimum size occurs, and (5) the possible interaction between a size limit and the projection of the maximum sustainable yield.
In employing yield-per-recruit analysis to the Atlantic yellowfin tuna fishery, two ap- proaches were taken — one approach makes use of a wide range of parameter estimates and a number of simplifying assumptions, but little data, and the other approach makes use of considerably more data, but is more confined in the parameter estimates and uses fewer of the simplifying assumptions. The general results of both approaches, assuming no dump- ing occurs, indicate that only minor increases in yield per recruit would occur if the size at recruitment is increased from our estimate of the present size at recruitment and fishing effort remains constant; an increase in fishing effort without changing other aspects of the fishery would not appreciably increase yield per recruit; and an increase in size at recruit- ment and in fishing effort would result in modest gains in yield per recruit. Specifically meeting the request of the International Commission for the Conservation of Atlantic Tunas, we recommended that a minimum size limit regulation in the vicinity of 55 cm (3.2 kg) be enacted.
The second regular meeting, in Madrid, Spain, on 2-7 December 1971, of the commission of ICCAT (International Commission for the Con- servation of Atlantic Tunas) authorized the "Council to recommend to the Contracting Par- ties that they prohibit landing of yellowfin weighing less than a minimum weight some- where between 3.2 and 10 kg." This recommen- dation was based on studies by members of the Subcommittee on Stock Assessment that showed that theoretically the size at first capture which maximizes the yield per recruit of yellow- fin is between 10 and 25 kg.
A special ICCAT working group on stock assessment of yellowfin tuna met in Abidjan, Ivory Coast, 12-16 June 1972, to consider fur- ther scientific aspects of size regulation and
other matters pertaining to the Atlantic yellow- fin fishery (ICCAT, 1972).- Studies on yield per recruit were presented by Hayasi, Honma, and Suzuki (1972) ;■' Joseph and Tomlinson (1972);^ and Lenarz and Sakagawa (1972)." A similar study was published by Wise (1972)
' Southwest Fisheries Center, National Marine Fisheries Service, NOAA, LaJolla, CA 92037.
- ICCAT. 1972. Report of the meeting of the special working group on stock assessment of yellowfin tuna (Abidjan, June 12-16, 1972). Manuscript on file at ICCAT General Mola 17, Madrid, 1 Spain.
•^ Hayasi, S., M. Honma, and Z! Suzuki. 1972. A com- ment to rational utilization of yellowfin tuna and albacore stocks in the Atlantic Ocean. Far Seas Fisheries Research Laboratory, Orido 1000, Shimizu, Japan. Unpublished manuscript.
-* Joseph, J., and P. K. Tomlinson. 1972. An evaluation of minimum size limits for Atlantic yellowfin. Inter- American Tropical Tuna Commission, La JoUa, Calif. Unpublished manuscript.
5 Lenarz, W., and G. Sakagawa. 1972. A review of the yellowfin fishery of the Atlantic Ocean. Southwest Fish- eries Center, National Marine Fisheries Service, La Jolla, Calif. Unpublished manuscript.
Manuscript accepted June 1973.
FISHERY BULLETIN: VOL. 72. NO. 1. 1974.
37
FISHERY BULLETIN, VOL. 72. No. 1
before the meeting. The report of the meeting may be considered as a summary of these pa- pers, which indicated that increases in size at recruitment would probably increase yield per recruit but not by more than about 10% .
The special ICCAT working group also ex- amined available evidence on the practicability of minimum size regulations. Scientists of the group were concerned that since the gears that fish for yellowfin in the Atlantic supposedly kill most fish that are captured, a minimum size regulation would reduce the number of small yellowfin that are landed but would not have the desired effect of reducing mortality rates of small yellowfin. This, of course, as- sumes that schools of yellowfin containing yel- lowfin less than any minimum size would actual- ly be set upon. In this connection the group noted that the conditions which must be met before minimum size regulations can be effec- tive are: (1) the fishermen must be able to estimate the size of yellowfin in a school, and (2) there must be little or no mixing of small yellowfin with large yellowfin within schools.
Very little evidence is available from the At- lantic on these subjects. Ten sami)les were pre- sented at the Abidjan meeting that indicated considerable mixing of small yellowfin (<5 kg) with large yellowfin (>5 kg) within schools. The working group also took note of a study on the subject by Calkins (1965) when size regula- tions were being considered by the lATTC (Inter-American Tropical Tuna Commission) for the yellowfin fishery in the eastei'n tropical Pacific. Calkins, working with only one hypo- thetical minimum size out of a range of 12.7 to 25.0 kg, concluded that a 12.7-kg size regulation would be seriously complicated by size varia- tion within sets. He also noted that a consid- erable amount of small yellowfin are often cap- tured in sets that include skipjack. Thus it ap- pears that it would not be possible to fish for skii)jack without killing some small yellowfin. Evidence based on the few samples from the Atlantic indicated that sets would include yellowfin tuna larger and smaller than 5 kg; thus even if a minimum size regulation were set at this value it would be difficult to prevent the capture offish smaller than 5 kg.
The working group recommended that more data should be collected on the subject from the Atlantic. The working group also noted
that a reduction in the size at first recruitment should be prevented and that minimum size regulations of 3.2 kg that have been passed by several African nations should help prevent a reduction in size at recruitment.
The population dynamics of Atlantic yellow- fin tuna are complex because the fishery is prosecuted by several types of gear: bait boats, small purse seiners, large purse seiners, and longliners. These gears tend to capture differ- ent sizes of fish and thus affect the population in different ways. FAO (1968) noted that long- line gear tends to capture large yellowfin while the other gears capture small yellowfin. Lenarz (1970).'' with more recent data, showed that American" purse seine gear tends to capture relatively more large yellowfin — in significant quantities — than was indicated for the earlier surface fishery. Joseph and Tomlinson (1972, see footnote 4) presented data that indicated small purse seiners of France-Ivory Coast- Senegal (FIS) tend to capture relatively more small yellowfin than the large FIS and Ameri- can purse seiners. The differences among size selectivity of the four gears necessitates con- sideration of the physical makeup of the fleet when e.xamining size regulations. Therefore, considerable attention was paid to this aspect of the problem during the study.
The above paragraph might be taken to imply that adequate data are available respecting the relative quantities and size distributions of fish caught by the various gears. It is our feeling that the adequacy of the data needs to be dem- onstrated. We cannot place much faith in the details of the relative size distributions per unit effort among the various fishing units, but we do feel that the general orders of magnitude are essentially correct. We should also point out that with the improvement in data over the last several years, the interpretations which accrue from the data and our appreciation of the considerable complexity of the fishery are more evident.
Definitions of Minimum Size
Because this paper discusses minimum size, it is necessary to define the term explicitly to
" Lenarz, W. 1970. Estimates of yield per recruit of Atlantic yellowfin tuna. Southwest Fisheries Center, National Marine Fisheries Service, La Jolla, Calif. Un- published manuscript.
" Refers to vessels registered in Canada, Panama, and the U.S.A.
38
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
avoid ambiguity and to prevent possible mis- applications of the results of this study. "Mini- mum size" may be viewed from two aspects: absolute minimum size and effective minimum size. Absolute minimum size is defined as the smallest fish in the catch and is related to the concept of knife-edged recruitment in defining the size at recruitment to the fishery. Recruit- ment is defined as the act of becoming vulner- able to fishing. In the case of knife-edged re- cruitment, no fish are vulnerable to fishing prior to the size at recruitment. Fish that are larger than the size at recruitment are full}^ vulner- able to fishing. Since most recruitment is size specific, hence sequential, the term effective minimum size is also needed. Effective mini- mum size is that size whose corresponding age is used as the lower bound for integration of the yield equation as if recruitment were knife- edged, and which gives the same yield per re- cruit as the sequential recruitment case.
Approaches to Yield - Per-Recruit Analysis
This paper examined several of the concepts involved in yield-per-recruit analyses because the question of what is the optimum minimum size for a given rate of exploitation is usually interpreted through such analyses. Both the classical approach, in which fishing mortality is constant with knife-edged reciiiitment. and the more complex approach, in which fishing mortality is size specific, are explored.
Throughout the paper we have intentionally kept mathematical notation to a bare minimum. We believe that most of the equations used are well known to readers actively involved in stock assessment. Readers who are not familiar with the equations can find excellent descrip- tions in the cited literature.
Employing the classical approach to yield- per-recruit analysis involves: (1) estimating the age or size at recruitment which represents an approximation of the current state of the fishery in terms of knife-edged recruitment; (2) finding the age or size at recruitment which maximizes the yield per recruit at a given level of fishing mortality; (3) imposing some regula- tion on the fishery such to achieve as its effec- tive minimum size, the age or size at reci-uit- , ment which maximizes the yield per recruit. The advice from the yield-per-recruit isopleth (in terms of the optimal age or size at recioiit-
ment) may be interpreted as either a knife- edged absolute minimum size or as an effective minimum size. Since for the fishery under con- sideration (and for many other fisheries as well) recruitment is not knife-edged, then we are talking about an effective minimum size. Now, on the other hand, if we assume that the abso- lute minimum size, the regulated size, and the effective minimum size are all the same, then we will have an inappropriate estimate of the yield per recruit, and the optimum may not be achieved. Somehow we need to determine the relationship between the effective minimum size and the regulated size; in some instances they can roughly be the same; but this equality will usually not obtain if the regulated size is chosen to be the absolute minimum size in the catch.
The more complex approach, which estimates size-specific fishing mortality, circumvents the first difficulty encountered in the classical ap- proach, i.e., determining a knife-edged approxi- mation to the current state of the fishery. The problem still remains, however, as to interpre- tation of the advice from the yield-per-recruit isopleth in terms of an effective minimum size. Joseph and Tomlinson (1972, see footnote 4) used the more complex approach in a recent study on minimum size regulations for the At- lantic yellowfin fishery. We have updated their analysis by using data made available at the Abidjan meeting and have also examined the sensitivity of the methodology to various sources of errors in the data.
DATA, PARAMETERS, AND COMPUTER PROGRAMS
Data
Catch- and length-frequency data for each type of gear for the 1967-71 period were ob- tained from the report of the meeting of the special ICC AT working group (Tables 10, 11, and 12 of ICCAT, 1972, see footnote 2) with the exception of length-frequency data of the 1967-68 FIS fishery and 1971 Japanese long- line fishery. Length frequencies for the 1967-68 FIS fishery were compiled from various ORSTOM (Office de la Recherche Scientique et Technique Outre-Mer) publications (Lenarz and Sakagawa, 1972, see footnote 5). Length
39
FISHERY BULLETIN, VOL. 12. NO. 1
frequencies from the 1971 Japanese longline fishery are assumed to be the same as those of the 1970 Japanese longline fishery; this as- sumi)tion appears justifiable because year to year changes in length frequencies from long- line fisheries tend to be less than differences in length frequencies between longline fisheries and surface fisheries.
Length-frequency data were available only from the Jai)anese longline fishery, FIS surface fisheries, and American large purse seine fishery. Thus it was necessary to make several assump- tions before estimating the length frequencies of the total catch of yellowfin in the Atlantic. Length frequencies for longline fisheries other than Japan are assumed to be the same as Japan's. Length frequencies for the bait boat and small purse seine fisheries other than FIS were assumed to be the same as the FIS fish- ery. Length frequencies for the large purse seine fisheries other than FIS and American were assumed to be the same as those two fisheries.
Parameters
The growth equation [L = 194.8 X (1 - g-0.42 (< - o.62))j presented in LeGuen and Sakagawa (1973) and length-weight relation- ship {W = 0.0000214L2-9736) given by Lenarz (19713)*^ were used, where L is fork length in cm, t is age in years, and W is weight in kg.
The annual instantaneous coefficient of nat- ural mortality (M) is a difficult parameter to estimate and due to a lack of data only pre- liminary estimates have been made for the pa- rameter in the Atlantic. We assume as most authors have that M is constant over the ex- ploited phase. Estimates of M = 2.61 and 1.50 for the Atlantic were made by Pianet and LeHir (1971) based on data from bait boats and seiners, respectively. These estimates seem unreason- ably high perhaps because their data were only from the Pointe Noire region which is a small area compared to the total region in the Atlan- tic where yellowfin tuna are found. Hennemuth (1961) estimated that M is 0.8 in the Pacific while Davidoff (1969) chose the upper bound
of Hennemuth's estimate, 1.0. Hennemuth's work was based on estimates of instantaneous coefficient of total mortality (Z) made from age compositions of catches by primarily bait boats and an estimate of instantaneous coefficient of fishing mortality (F) from Schaefer (1957). Since bait boats appear to be selective for small yellowfin, F and Z are not constant, and meth- ods of ageing yellowfin have not been proven correct, Hennemuth's estimate must be con- sidered a first approximation. However, his estimate seems reasonably consistent with what is thought to be the life span of yellowfin. We assumed for the purposes of our calculations here that M is 0.8 as is conventional (based on Hennemuth's work in the Pacific); we also used values of 0.6 and 1.0 to encompass what we believe is the range of reasonable values.
Pianet and LeHir (1971) also estimated an average F of 0.88 for the segment of the At- lantic yellowfin tuna population that is exploit- ed in the Pointe Noire region. As we have indi- cated, their estimate is not representative for the population as a whole.
Our range of estimates of Z for 1967-71 is 0.91 to 1.82 (Lenarz and Sakagawa, 1972, see footnote 5). If we assume that M = 0.8 for the Atlantic population, then F is 0.11 to 1.02. We believe that F is about 0.6 for recent years. However, we used a range of F values in our study.
Computer Programs
Most of the calculations were performed on the Burroughs 6700-' computer at the Univer- sity of California at San Diego. Programs used in the analysis, except for FRG708 (Paulik and Bayliff, 1967), were written by the authors; they are as follows:
1. Simplified Beverton and Holt yields per recuit— YPER.
2. Accuracy of knife-edged approximations of age at entry and interactions between mini- mum size and catch quota regulations — GXPOPS.
3. Yield-per-recruit isopleths under knife- edged recruitment — FRG708.
** Lenarz, W. 1971a. Length-weight relations for five Atlantic scombrids. Southwest Fisheries Center, National Marine Fisheries Service, La Jolla, Calif. Unpublished manuscript.
" Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.
40
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
4. Size-specific rates of fishing mortality — COHORT.
5. Yield-per-recruit isopleths for multigear fisheries with size-specific F — MGEAR.
6. Optimum size at recruitment under differ- ent levels of effort by two gears — OPSIZE.
ANALYSIS
As previously mentioned in the introduction, we use two approaches in analyzing the data, the knife-edged recruitment approach and the size-specific F approach.
Knife-Edged Recruitment Approach Introduction
Two commonly used models for computing yield per recruit and determining the size at recruitment which maximizes yield per recruit are those of Beverton and Holt (1957) and Kicker (1958). We employed both models for knife-edged approximation analyses — the sim- plified Beverton and Holt model, making use of a wide range of parameter estimates or extra- polations from fisheries for similar species, and the Ricker model, making use of the best param- eter estimates and giving a more detailed an- alysis of yield per recruit. We used the Ricker model instead of the Beverton and Holt model for calculating yield-per-recruit isopleths be- cause the Ricker model allows the use of expo- nents in the length-weight relationship with values other than 3. It is important to stress that the material in the simplified Beverton and Holt model involves fewer assumptions than the material in subsequent sections. This is important because as our approach becomes more complex the data requirements become more rigorous. It can be argued that we have sufficient data for this simplified approach. In the more complex approaches this assertion be- comes more tenuous; because we use more as- sumptions in the more complex approaches we do not necessarily obtain more information, even though it may appear that way. However, it should be noted that the assumption of a constant rate of mortality over the fishable life span contained in the simplified approach may be important, and we believe that it is not ful- filled. These analyses are followed by sections discussing the problems of determining the
proper parameters which represent the cur- rent situation of the fishery.
Simplified Beverton and Holt Model
The Beverton and Holt yield-per-recruit model may be simplified such that relative yield per recruit, Y\ is a function of three ratios:
C = i,:iL^
Q = MIK
E = FI(F + M)
Y'= YI(RW^)
and where // is the size (length) at recruit- ment, W^ , L^ , and K are parameters of the von Bertalanffy growth equation, Y is yield in weight, and R is recruitment. Y' is tabulated in Beverton and Holt (1966), but more extensive calculations were performed with program YPER.i" Beverton and Holt (1959) concluded that, within reason, there exists a common ratio between M and K within related species groups. Therefore, a range of estimates for the various parameters is utilized along with other information obtained by examining parameter estimates for M and K for yellowfin tuna from areas other than the Atlantic.
The range of values for the various parameters is as follows: K = 0.28 to 0.53 and L^ = 175.2 to 223.0 cm from LeGuen and Sakagawa (1973), Z = 0.91 to 1.82 from Lenarz and Sakagawa (1972, see footnote 5), and M = 0.6 to 1.0. From these ranges of e.stimates, a maximum range for E is 0.0 to 0.67 and for Q is 1.13 to 3.57. Using our most reasonable parameter estimates of K = 0.42, M = 0.8, and Z = 1.4, however, a rea- sonable range for E and Q was established by allowing either the numerator or denominator of the ratio to be one of our most reasonable estimates — the reasonable ranges are E = 0.12 to 0.56 and Q = 1.42 to 2.86. With K = 0.42, M = 0.8, and Z = 1.4, our most reasonable es- timates of £■ and Q are 0.43 and 1.9. respectively. Table 1 contains optimal values of size (cm) at recruitment, /*/, for the maximum range of estimates of E and Q (deleting the impossible E = 0.0) for the range and most reasonable es- timates of L^. The dashed lines enclose the
,1 f.^n.A"'"^ ^^'"^^ °f '•• Table lib of Beverton and Holt (1966) was slightly higher than computed by YPER- this may be due to differing methods of rounding
41
FISHERY BULLETIN. VOL 72. NO. 1
Table \. — Optimal values of .size at recruitment (cm) as a function of the rate of exploitation (E) and the ratio of M to K (Q) for three estimates of L^..'
E Q 0.1 0.2 0.3 0.4 0.5 0.6 0.7
= 175.2 cm
|
1.0 |
56.6 |
|
1.5 |
49.4 |
|
2.0 |
43.8 |
|
2.5 |
39.4 |
|
3.0 |
35.9 |
|
3.5 |
32.9 |
|
1.0 |
62.9 |
|
1.5 |
54.9 |
|
2.0 |
48.7 |
|
2.5 |
43.8 |
|
3.0 |
39.9 |
|
3.5 |
36.6 |
|
1.0 |
72.0 |
|
1.5 |
62.9 |
|
2.0 |
55.8 |
|
2.5 |
50.2 |
|
3.0 |
45.7 |
|
3.5 |
41.9 |
|
73.1 |
84.4 |
94.3 |
102.3 |
109.5 |
|
64.1 |
74.8 |
83.4 |
90.8 |
97.1 |
|
57.1 |
66.9 |
74.8 |
81.5 |
87.2 |
|
51.7 |
60.4 |
67.8 |
73.9 |
79.4 |
|
47.1 |
55.4 |
62.0 |
67.6 |
72.7 |
|
""43.3 "■ |
51.0 |
57.1 |
62.4 |
66.9 |
= 194.8 cm
|
81.2 |
94.3 |
104.8 |
113.8 |
121.8 |
|
r"7r3~ ■ |
83.2 |
92.7 |
100.9 |
107.9 1 |
|
1 63.5 |
74.4 |
83.2 |
90.6 |
97.0 1 |
|
j 57.5 |
67.2 |
75.4 |
82,2 |
88,2 j |
|
1 52.4 |
61.6 |
69.0 |
75.2 |
80.8 1 |
|
—js--- |
56.7 |
63.5 |
69.4 |
74,4 |
= 223.0 cm
115.8 102.8 92,5 84.1 77,1 71.1
128.8
114,4
102,8
93.5
85.7
79.1
147,4 130,9 117,7 107,0 98,1 90.5
' Dashed lines encompass our reasonable range of values; our most reasonable estimate.
underlined value is
reasonable range of estimates (deleting the un- reasonably low E — 0.12), and the underlined value in the center of Table 1 is our most reason- able estimate. One can see in Table 1 that the values are all greater than the approximate absolute minimum size of 32.5 cm'^ for the At- lantic yellowfin tuna fishery over the range of the estimates of L^ .
For the moment let us assume that recruit- ment is knife-edged at 32.5 cm (0.67 kg) and that the fishery can be regulated such to obtain a knife-edged recinaitment at any desired size. Therefore, the maximum possible increases in yield per recruit may be computed. Our smallest reasonable values for optimal size at recruit- ment are 47.1 cm (2.0 kg), 52.4 cm (2.8 kg), or 60.0 cm (4.1 kg) depending on L^. The respec- tive predicted values of yield per recruit are 2.0% , 3.1% , and 4.3% higher than when size at recruitment is 32.5 cm. Our largest reasonable estimates of optimal size at recruitment are 97.1 cm (17 kg), 107.9 cm (24 kg), or 123.5 cm (36 kg). The respective predicted increases in yield
" The value of 32.5 cm represents our selection for an approximate absolute minimum size for the Atlantic yellowfin tuna fishery, which also agrees with that chosen by Joseph and Tomlinson ( 1972, see footnote 4).
per recruit are 65% , 73% , and 82% . The predict- ed increase in yield per recruit using all of our most reasonable parameter estimates, i.e., rais- ing 32.5 cm to 83.2 cm (11 kg), is 23%. The bounds on an increase in yield per recruit, 2% to 82% , and the most likely value of 23% , are estimated under the assumptions of knife-edged recruitment, and that size at recruitment rep- resents an absolute minimum size. The Atlantic yellowfin tuna fishery, however, does not have knife-edged recruitment.
We used equation lb of this paper to obtain our most reasonable estimate of the 1967-71 average effective minimum size for the Atlantic yellowfin tuna fishery from average lengths given in Table 15 of Lenarz and Sakagawa (1972, see footnote 5). The estimate of average effective minimum size is about 55 cm (3.2 kg). Nearly all the values within the dashed lines in Table 1, however, are greater than 55. The only smallest reasonable estimate of optimal effective minimum size greater than 55 cm is 60.0 cm with Lqo — 223.0 cm. An increase from 55 to 60.0 cm would give an increase in yield per re- cruit < 0.2% . The large.st reasonable estimates of optimal effective minimum size predict increases in yield per recruit of 28% , 36% , or 45% with in-
42
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
creases from 55 cm to 97.1, 107.9, and 123.5 cm, respectively depending on L^ . The increase in yield per recruit by increasing the effective minimum size from 55 to 83.2 cm, our most reasonable estimate, is only 7.9% .
From the above analysis using a wide range of parameter estimates, we can conclude with reasonable assurance that virtually any increase in the effective minimum size will cause an in- crease in yield per recruit. Our most likely estimate of this increase in yield per recruit is only 7.9% which is bounded, with reasonable parameter estimates, by 0% and 45% .
Ricker Model
Ricker model yield-per-recruit isopleths were calculated using values of M of 0.6, 0.8. and 1.0 to illustrate our estimates of actual (rather than relative) yield per recruit (Figures 1, 2, and 3). As will be mentioned in the next section it is difficult to estimate the location of the fishery on the graphs, i.e., when fishing mortality is size specific it is not a trivial matter to make reasonable estimates of age at recruitment, t^, and a constant total mortality coefficient, Z. Our most reasonable estimates, taken from Lenarz and Sakagawa (1972, see footnote 5), of these parameters are: t '. is 1.41 yr and Z is 1.4.
0.5 10 1.5 2.0 2.5 30
INSTANTANEOUS FISHING MORTALITY (F)
35
5 10 15 2,0 2 5
INSTANTANEOUS RATE OF FISHING MORTALITY (F)
Figure 2. — Yield-per-recruit isopleths as functions of fish- ing mortality and age (and weight) at recruitment when M = 0.8.
-60.5
48.0
229
Figure 1. — Yield-per-recruit isopleths as functions of fish- ing mortality and age (and weight) at recruitment when M = 0.6.
5 10 1.5 20 25
INSTANTANEOUS RATE OF FISHING MORTALITY (F)
Figure 3. — Yield-per-recruit isopleths as functions of fish- ing mortality and age (and weight) at recruitment when M = 1.0.
The results (Figures 1, 2, and 3) show, for example, that with M = 0.6 and Z remaining constant (1.4), an increase in age at recruitment from 1.41 to 1.83 yr (or 77.5 cm) raises the yield per recruit about 20% ; if iV/ = 0.8, the same change raises the yield per recruit on the order of 10% ; and if M = 1.0, the same change does
43
FISHERY BULLETIN, VOL. 72. NO. 1
not change yield per reci*uit. If age at reciniit- ment is held constant and fishing mortality is doubled, when M = 0.6 yield per reci-uit de- creases by some 20% ; when M = 0.8 yield per recruit increases on the order of 5% ; and when M = 1.0 yield per recruit increases about 30%. If effort is doubled and age at recruitment is raised to 1.83 yr, when M = 0.6 or M = 0.8 yield per recruit increases on the order of 20% ; and when M = 1.0 yield per recruit increases by about 40% .
Estimation of t
r
In employing a knife-edged approximation to size-specific recruitment protracted over some time period, the first problem is to determine the proper age at recruitment {t^') such that the integration reflects the same yield per re- cruit as the size-specific recruitment case. There are two problems in doing so. First, there are two values for t^.' that will give the same yield per recruit as the size-specific recruitment case, unless eumetric fishing obtains. Often, however, this may be of little consequence, since one of the two values for t ' could be obviously infea- sible. Second, t ' will depend on the fishing mortality.
Two estimators of t ' are provided, at least implicitly, by Beverton and Holt (1957): (1) the age corresponding to the mean selection length, and (2) the resultant of a formula depending on Z and the average age, T (or average length. /). in the catch. The mean selection length is the 50% selection length if the selection curve is symmetrical, and it is not dependent on the magnitude of the fishing mortality coefficient, F. The second estimator of t ' is
r
t; - 1 -HZ
or, in terms of length
i; = J-K{L^-J)jZ.
(la)
(lb)
These two equations were obtained from manip- ulations of the Beverton and Holt yield equation. Several computations of yield per recruit with the program GXPOPS were made utilizing F = 0.1 and F - 2.0. M = 0.8, the von Bert- alanffy equation for Atlantic yellowfin tuna, and an arbitrary age-specific selection curve (Figure 4) in order to demonstrate the two
1.0,-
0.8
06
04
0.2
50% SELECTION AT 21 mo.
|<— F = 20 tr' = 24 mo
F = 0 I tr = 19 mo.
10
20
30 40
AGE (mo)
50
60
70
Figure 4. — Arbitrary age-specific recruitment curve.
problems and to evaluate the two estimators of t ', . At F — 0.1, the values of t ! giving the same yields per recruit as the selection curve are <8 mo (^q of the von Bertalanffy growth curve is 7.48 mo) or 24 mo, and 19 or 45 mo for F = 2.0. Since the state of the simulated fishery is not eumetric for either value of F, there are two knife-edged approximation locations. The effect of the magnitude of F on the true t ' is obvious, with the lower value increasing from <8 to 19 mo and the upper value increasing from 24 to 45 mo as F is changed from 0.1 to 2.0. The reasonable values for t ' to approx- imate the selection curve, however, are 24 mo for F = 0.1 and 19 mo for F = 2.0, a change of 5 mo.
Estimator 1, the mean selection age, is 21 mo and is shown along with the reasonable values in Figure 4. Using 21 mo for t^' would result in yields per recruit that are 4% and 15% too high for F = 0. 1 and F = 2.0 respectively. Estimator 1 does not change with F, of course, but in this case it lies intermediate between the true t^' values. Estimator 2 gives 19 mo for F = 0.1 and 18 mo for F = 2.0. We emphasize that this estimator does depend on the magni- tude of F.
Neither estimator is exact in this examj^le where the catches, their ages, and the selection curve are known without error. This places doubt on their estimates from the usual catch at age data where considerable random error would be involved. Encouraging, though, is that both estimators indicate the proper direction that the fishery's selectivity should proceed to approach the optimal yield per recruit — about
44
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
15 mo for F = 0.1 and 30 mo for F = 2.0. Since estimator 1 requires size-selective data not fre- quently available and does not respond to changes in F, estimator 2 appears to be the most attractive for knife-edged approximations. The Atlantic yellowfin tuna fishery, however, has a much more complex recruitment pattern and size-specific F than this simple example owing to the diverse gear types. The mix of relative F among the various gear types makes the determination of the appropriate current t ' somewhat tenuous.
r Estimation of Constant Z
The yield-per-recruit isopleths shown in Fig- ures 1, 2, and 3 were calculated under the assumption that fishing mortality and Z are constant after the fish are recruited. The value of Z was also estimated under the same assump- tion. The section on size-specific fishing mortal- ity will indicate that F is not a constant, but is related to size. Thus our estimate of a constant Z may not be realistic but may be a more reasonable approach to estimating yield per recruit than the size-specific F approach given the quality of the data. It is the average of values of Z estimated for the FIS bait boat and purse seine fisheries (Lenarz and Sakagawa, 1972, see footnote 5). The size-specific F section indi- cates that F decreases with size for bait boats and increases with size for purse seiners. Bever- ton and Holt (1956) gave examples that indi- cated that when F decreases with age, constant Z will be overestimated and when F increases with age, constant Z will be underestimated. Hopefully we have obtained a reasonable esti- mate by taking the average of Z's for the two gears.
Size-Specific I Approach Estimates of Length Frequencies
Length frequencies, numbers of yellowfin caught by 5-cm intervals starting at 35 cm (32.5 cm ^ fork length <37.5 cm), were estimated for each gear and the total fishery for two overlap- ping periods, 1967-71 and 1969-71 (Figure 5). The first period was used with the hope that the effect caused by unequal strength of year classes would be minimized by averaging. The second period was used because it was felt that
700r
o 1969-71 • 1967 - 71
40
60
80 100 120
FORK LENGTH (cm.)
140
160
180
Figure 5. — Average length frequencies for the Atlantic yellowfin tuna fisheries for two periods, 1967-71 and 1969-71.
300
Q 250 UJ
o
z <
-• 200
z li.
3 150
_)
UJ
>-
\k 100
o o o
50
OL
o BAITBOAT
• SMALL PURSE SEINE A LARGE PURSE SEINE A LONGLINE
40
60
140
80 100 120
FORK LENGTH (cm)
Figure 6. — Average length frequencies (1967-71) tic yellowfin tuna caught by four gear types.
160
180
of Atlan-
the data are more accurate. Length frequencies of the two periods are quite similar and produce similar estimates of size-specific fishing mortal- ity and estimates of yield per recruit. Thus, to avoid redundancy, only the data for the 1967-71 period are used. Figure 6 and Table 2 show the length frequencies for each gear. The curves are as described earlier (see introductory section.)
Estimates of Size-Specific Fishing Mortality
Size-specific instantaneous coefficients of fish- ing mortality were estimated with the method of Gulland (1965) and Murphy (1965) as suggested
45
FISHERY BULLETIN, VOL. 72. NO. 1 Table 2. — Basic data on size (age) composition of catch of yellowfin tuna from the tropical Atlantic Ocean.
|
Weight |
Age |
1967-71 average |
> number of yell |
Dwfin landed |
|||
|
Midpoint of |
at beginning |
ot beginning |
|||||
|
size interval |
of interval |
of interval |
Small purse |
Large purse |
|||
|
(cm) |
(kg) |
(yr) |
Bait boats |
seiners |
seiners |
Longliners |
Total |
|
35 |
0.67 |
1 .0579 |
1,886 |
372 |
100 |
2,358 |
|
|
40 |
1.03 |
1.1325 |
14,551 |
5,445 |
9,057 |
29,053 |
|
|
45 |
1.49 |
1 .2093 |
72,972 |
21,782 |
28,372 |
123,126 |
|
|
50 |
2.08 |
1.2888 |
246,924 |
89,614 |
36,684 |
7 |
373,229 |
|
55 |
2.79 |
1.3710 |
245,206 |
146,883 |
83,153 |
22 |
475,264 |
|
60 |
3.66 |
1.4562 |
251,017 |
110,755 |
59,648 |
451 |
421,871 |
|
65 |
4.69 |
1.5445 |
165,328 |
42,427 |
35,891 |
647 |
244,293 |
|
70 |
5.90 |
1 .6363 |
197,855 |
49,929 |
26,992 |
2,151 |
276,927 |
|
75 |
7.30 |
1.7317 |
143,885 |
36,942 |
23,263 |
5,435 |
209,525 |
|
80 |
8.90 |
1.8310 |
128,810 |
37,082 |
15,528 |
5,694 |
187,114 |
|
85 |
10.72 |
1.9348 |
89,637 |
31,143 |
13,338 |
12,025 |
146,143 |
|
90 |
12.77 |
2.0432 |
64,128 |
31,135 |
9,818 |
13,049 |
118,130 |
|
95 |
15.06 |
2.1568 |
70,422 |
22,248 |
10,062 |
1 1 ,665 |
114,397 |
|
100 |
17.61 |
2.2761 |
63,619 |
36,483 |
13,323 |
15,074 |
128,499 |
|
105 |
20.43 |
2.4017 |
45,582 |
48,274 |
11,647 |
34,071 |
139,574 |
|
110 |
23.54 |
2.5343 |
36,414 |
42,283 |
24,296 |
40,209 |
143,202 |
|
115 |
26.95 |
2.6748 |
29,227 |
21,268 |
21,466 |
44,034 |
115,995 |
|
120 |
30.67 |
2.8240 |
18,877 |
18,311 |
15,144 |
42,859 |
95,191 |
|
125 |
34.72 |
2.9832 |
22,228 |
23,711 |
15,018 |
57,358 |
118,915 |
|
130 |
39.10 |
3.1538 |
15,152 |
20,612 |
16,238 |
58,544 |
1 10,546 |
|
135 |
43.84 |
3.3376 |
7,142 |
18,304 |
18,504 |
44,690 |
88,640 |
|
140 |
48.95 |
3.5368 |
4,137 |
15,790 |
13,569 |
52,070 |
85,566 |
|
145 |
54.43 |
3.7542 |
3,393 |
17,301 |
17,886 |
55,582 |
94,162 |
|
150 |
60.31 |
3.9935 |
3,459 |
20,222 |
16,711 |
45,648 |
86,040 |
|
155 |
66.60 |
4.2595 |
1,511 |
12,057 |
14,926 |
39,108 |
67,602 |
|
160 |
• 73.30 |
4.5590 |
793 |
8,754 |
10,678 |
24,489 |
44,714 |
|
165 |
80,44 |
4.9017 |
634 |
7,803 |
6,633 |
13,659 |
28,729 |
|
170 |
88.03 |
5.3021 |
327 |
2,470 |
2,918 |
6,265 |
1 1 ,980 |
|
175 |
96.07 |
5.7838 |
209 |
2,132 |
1,383 |
241 |
3,965 |
|
180 |
104.59 113.60 |
6.3883 7.2004 |
49 |
1,429 |
361 |
55 |
1 ,894 |
|
Total |
1,945,374 |
942,961 |
573,207 |
625,102 |
4,086,645 |
by Lenarz ( 1971b). '^ We followed the modifica- tion of Joseph and Tomlinson (1972, see foot- note 4) by using the inverse of the von Bertalanffy growth equation to convert size distributions to age distributions. This method assumes that there is a reasonably accurate relationship be- tween length and age of yellowfin tuna. This assumption has not been verified. Ageing by modal progression would probably be more satis- factory, if more complete length composition data were available on a monthly or quarterly basis.
The reverse iterative i)rocedure with com- puter program COHORT and M = 0.8 was used to estimate size-specific values of fishing mortal- ity (F) starting at the 180-cm interval. Four initial values of F were tried: 0.2, 0.4, 0.6, and 0.8 (Figure 7). Estimates of F tend to converge
as size of the yellowfin tuna decreases with the range of initial values tried as is characteristic
'2 Lenarz, W. 1971b. Yield per recruit of Atlantic
yellowfin tuna for multigear fisheries. Southwest Fisheries
Center, National Marine Fisheries Service, La Jolla. Calif. Unpublished manuscript.
>| ' I I I I I I Ill
40 60 80 100 120 140 160 180
FORK LENGTH (cm.)
Figure 7. — Estimates of size-specific instantaneous fishing mortality coefficients (F) with several initial F values.
46
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
of the methodology (Tomlinson, 1970). Calcula- tions of yield per reciniit using initial values of F of 0.2 and 0.8 are shown in Figures 8 and 9 as functions of initial values of F, effort, and size at recioiitment. The values of yield per recruit do not vary significantly (<10%) with changes in the initial values of F, and the rela- tive values are quite similar. Values of size speci- fic F are shown for each gear in Figure 10 when initial values of F are 0.2 and 0.8. When the initial value of F is 0.8. values of F for small purse seiners increase sharply with size from 170 to 180 cm. This does not occur when the initial value of F is 0.2. Intuitively we do not expect an increase in F with size past 170 cm and thus choose to use the results when the initial value of F is 0.2 in the remainder of the
0.5-
7i-
O INITIAL F = 0.8 • INITIAL F = 0,2
I I I I
J I
10 15 20 2 5
MULTIPLIER OF EFFORT
30
35
Figure 8. — Yield-per-recruil (kg) of Atlantic yellowfin tuna, when size at recruitment is 32.5 cm, as a function of the multipUer of fishing effort.
32.5 52.5 72.5 92.5 112.5 1325
FORK LENGTH AT RECRUITMENT (cm.)
Figure 9. — Yield-per-recruit (kg) of Atlantic yellowfin tuna, with the current level of fishing effort, as a function of length at recruitment.
>-
_l <
I-
cr o
to
3
o
<
<
O BAITBOAT
• SMALL PURSE SEINE A LARGE PURSE SEINE A LONGLINE
80 100 120 140
FORK LENGTH (cm)
Figure 10. — Estimates of size-specific instantaneous fish- ing mortality coefficients (F) by gear type when initial values of F are ( A) F = 0.2. ( B) F = 0.8.
paper. Validity of the estimates of F depends on the validity of the assumption that recruitment has been fairly constant for the cohorts included in the analysis. The special ICCAT working group noted that the cohort which entered the surface fisheries in 1969 appears to be weaker than the following two cohorts (ICCAT, 1972. see footnote 2). Although inclusion of 5 yr of data in the analysis may minimize the source of error, future studies should examine the sensi- tivity of the results to errors of this type.
Estimates of Yield Per Recruit
Results of the yield-per-recruit calculations using the estimates of size-specific F when the initial value of F is 0.2 and with M = 0.8 are shown by gear in Table 3. Yield-per-recruit isopleths and the line of eumetric fishing (size at recruitment, / ^, which maximizes yield per recruit at a given effort) for the entire fishery
47
Table 3. — Estimates of yield per recruit (kg) when M = 0.8, initial F
Sakagawa (1973) is used.
FISHERY BULLETIN, VOL. 72, NO. 1 0.2, and growth curve of LeGuen and
|
BAIT ROATS |
||||||||
|
MINIMUM t;i7E |
MULTJOLIFO OF FFrOPT |
|||||||
|
CM KG |
0.? |
0.4 |
O.A 1.0 1.4 |
1.8 |
2.0 |
a.s |
3.0 |
3.5 |
|
12?. S |
34.6 |
|
117. S |
30.6 |
|
U2.5 |
26.9 |
|
107. S |
23. S |
|
10?. 5 |
20.4 |
|
97.5 |
17.6 |
|
9?. 5 |
15.0 |
|
87.5 |
12.7 |
|
S?.5 |
10.7 |
|
77.5 |
•3.9 |
|
7'. 5 |
7.3 |
|
67.5 |
5.9 |
|
62.5 |
4.7 |
|
57.5 |
3.7 |
|
52.5 |
2.8 |
|
47.5 |
2.1 |
|
42.5 |
1.5 |
|
37.5 |
1.0 |
|
32.5 |
0.7 |
O.OR 0.09
o.n
0.13 O.IS 0.17 0.19 0.20 0.22 0.24 0.26 0.27
29 30 31 31
0.31 0.31 0.31
0.15 0.17 0.21 0.24 0.27 0.31
,35 ,38 ,41 ,45 ,48
O.Sl
0.53 0.56
57 5ft 5ft
21 24 29 33
38
0.58 0.58
0.44 0.50 0.54 0.58 0.63 0.68 0.72 0.75 0.78 0.79 O.ftO O.ftO 0.80 0.80
0.31 0.36
,43 ,50 ,57 ,66
,75 ,81 ,88
0.95
.02 .08 .12 .15 .15
1.15 1.15 1.15 1.15
0.39 0.46 0.55 0.64 0.73 0.85 0.96 1.04 1.12 1.22
30 38
1.41 1.43 1.42 1.42 1.41 1.41 1.41
0.46 0.54 0.65 0.75 0.86 1.01 1.15 1.24 1.34 1.45 1.54' 1.62 1.65 1.66 1.63 1.61 1.60 1 .60 1 .60
0.49 0.5ft 0.69 0.80 0.92 1.08 1.23 1.32 1.43 1.55 1.64 1.73 1.76 1.76 1.72 1.69 1.6ft 1.67 1.67
0.56 0.66 0.80 0.92 1.06 1.24 1.41 1.52 1.64 1.78 1.87 1.96 1.98 l."36 1.R8 1.84 1.82 1.81 1.81
0.62 0.71
o.8q
1.0? 1.17 1.38 1.58 1.69 1.8? 1.97 2.07 2.14 2.16 2.11 2.00 1.94 1.91 1.90 1.90
0.68 0.80 0.96 l.U 1.27 1.50 1.72 1.84 1.98 2.13 2.?3
30 30 22
08 00
1.97 1.96 1.95
SMALL PU9SF 5FINJEWS
MINIMUM SI7E
MULTIPLIFP OF FFFORT
CM
KG
|
127.5 |
34.6 |
|
117.5 |
30.6 |
|
112.5 |
26.9 |
|
107.5 |
2 3.5 |
|
102.5 |
20.4 |
|
Q7.5 |
17.6 |
|
o='.5 |
15.0 |
|
87.5 |
12.7 |
|
82.5 |
10.7 |
|
77.5 |
8.9 |
|
72.5 |
7.3 |
|
67.5 |
5.9 |
|
6?. 5 |
4.7 |
|
57. S |
J. 7 |
|
5?. 5 |
2. ft |
|
47.5 |
2.1 |
|
42.5 |
1.5 |
|
37.5 |
1.0 |
|
32.5 |
0.7 |
0.2
0.34 0.35 0.36 0.3fl 0.40 0.41 0.41 0.42 0.42 0.43 0.43 0.43 0.43 0.43 0.44 0.44 0,44 0.44
0.4
0.58 0.60 0.61 0.64 0.67 0.69 0.70 0.71 0.71 0.71 0.71 0.72 0.71
,71 ,72 ,71 ,71 ,71 ,71
0.6
0.75 0.77 0.79 0.83 0.87 0.89 0.90 0.91 0.91 0.91 0.91 0.91 0.90 0.90 0.89 0.89 0.«8 0.88 0.88
1.0
0.97 0.99 1.01 1.06 1.1? 1.14 1.15 1.16 1.16 1.15 1.14 1.13 1.11 1.10 1.08 1.06 1.06 1.06 1.06
1.4
1.09 1.11 1.13 1.20 1.27 1.30 1.30 1.31 1.30 1.29 1.27 1.24 1.22 1.19 1.16 1.13 1.12 1.12 1.12
1.8
1.16 1.18 1.20 1.28 1.37 1.40 1.39 1.40 1.39 1.37 1.34 1.30 1.27 1.23 1.19 1.15 1.14 1.13 1 . 13
2.0
1.19 1.71 1.73 1.32 1.41 1.44 1.43 1.44 1.43 1.40 1 .36 1.32 1 .78 1.74 1 .20 I.IS 1.14 1.13 1.13
2.5
1.24 1.27 1.28 1.38 1.49 1.52 1.50 1.51 1 .49 1.45 1.41 1.35 1 .30 1.24 1.19 1.14 I. 11 1.11 1.11
3.0
1 .28 1. 30 1.31 1.43 1.55 1.59 1.56 1.56 1.53 1.49 1.43 1.36 1.29 1.23 1.17 l.U 1.08 1.08 1.0«
3.5
1.31 1.33 1.34 1.47 1.60 1.64 1.61 1.60 1.57 1.51 1.44 1.35 1.28 1.21 1.14 1.07 1.05 1.04 1.04
MINIMUM SI7E
CM
KG
0.4
L4RGF PURSE SEINERS MULTTPLIEP OF EFFORT
0.6
1.0
1.4
1.8
2.5
3.0
3.5
|
122.5 |
34.6 |
0.31 |
0.54 |
0.69 |
0.89 |
0.99 |
1.05 |
1.07 |
1.10 |
1.1? |
1.12 |
|
117.5 |
30.6 |
0.32 |
0.55 |
0.71 |
0.90 |
1.01 |
1.06 |
1 .08 |
1.11 |
1.1? |
1.13 |
|
112.5 |
?6.9 |
0.33 |
0.56 |
0.73 |
0.92 |
1.03 |
1.09 |
1.11 |
1.14 |
1.16 |
1.17 |
|
107.5 |
23.5 |
0.34 |
0.58 |
0.74 |
0.94 |
1.04 |
1.10 |
1.12 |
1.15 |
1.17 |
1.18 |
|
102.5 |
20.4 |
0.14 |
0.58 |
0.74 |
0.93 |
1.0? |
1.06 |
1.08 |
I.IO |
1.10 |
1.10 |
|
97.5 |
17.6 |
0.35 |
0.58 |
0.74 |
0.9? |
1.00 |
1.04 |
1.05 |
1.06 |
1.06 |
1.06 |
|
92.5 |
15.0 |
0.35 |
0.58 |
0.73 |
0.91 |
0.99 |
1.02 |
1.03 |
1.03 |
1.03 |
1.02 |
|
ft7.5 |
12.7 |
0.35 |
0.58 |
0.73 |
0.90 |
0.97 |
1 .00 |
1 .00 |
1.00 |
0.99 |
0.97 |
|
82.5 |
10.7 |
0.35 |
0.5ft |
0.73 |
0.89 |
0.96 |
0.98 |
0.9B |
0.97 |
0.95 |
0.93 |
|
77.5 |
8.9 |
0.35 |
0.58 |
0.72 |
0.88 |
0.93 |
0.45 |
0.95 |
0.^3 |
0.91 |
0.88 |
|
?2.5 |
7,3 |
0.35 |
0.57 |
n.7? |
0.86 |
o.q? |
0.92 |
0.92 |
0.90 |
0.87 |
0.84 |
|
67.5 |
5.9 |
0.35 |
0.57 |
0.71 |
0.85 |
0.89 |
0.89 |
0.88 |
0.86 |
0.87 |
0.79 |
|
6 7. S |
4.7 |
0.35 |
0.57 |
0.71 |
0.84 |
0.87 |
0.87 |
0.86 |
0.83 |
0.80 |
0.76 |
|
57.5 |
3.7 |
0.35 |
0.57 |
0.70 |
0.8? |
O.ftS |
0.84 |
0.82 |
0.79 |
0.75 |
0.71 |
|
57.5 |
2.8 |
0.35 |
0.57 |
0.69 |
0.80 |
O.ft? |
0.80 |
0. 79 |
0.75 |
0.71 |
0.67 |
|
47.5 |
2.1 |
0.35 |
0.56 |
0.68 |
0.78 |
0.79 |
0.77 |
0.75 |
0.71 |
0.66 |
0.62 |
|
47.5 |
1.5 |
0.35 |
0.56 |
0.68 |
0.78 |
0.79 |
0.76 |
0.7S |
0.70 |
0.65 |
0.61 |
|
37.5 |
1.0 |
0.35 |
0.56 |
0.68 |
0.78 |
0.79 |
0.76 |
0.75 |
0,70 |
0.6S |
0.61 |
|
37.5 |
0.7 |
0.35 |
0.56 |
0.68 |
0.78 |
0.79 |
0.76 |
0.74 |
0.70 |
0.65 |
0.61 |
48
LENARZ ET AL.: YIELD PER RECRUIT OF ATLANTIC YELLOWFIN TUNA
Table 3. — Estimates of yield per recruit (kg) when M = 0.8. initial F = 0.2, and growth curve of LeGuen and
Sakagawa ( 1973) is used. — Continued.
|
LONG LINFRS |
|||||||||||
|
MINIMUM |
SIZE |
MUl TIPLIEC OF FFFOPT |
|||||||||
|
CM |
KG |
0.? |
0.4 |
0.6 |
l.O |
1.4 |
1.8 |
2.0 |
2.5 |
3.0 |
3.5 |
|
1??.5 |
^'..f. |
0.80 |
1.40 |
1.8*. |
2.49 |
2.87 |
3.12 |
3.21 |
3.38 |
3.49 |
3.57 |
|
117.5 |
30.6 |
0.82 |
1.44 |
1.90 |
2.53 |
2.90 |
3.14 |
3.23 |
3.38 |
3.47 |
3.54 |
|
11?. S |
?6.<5 |
0.84 |
1.46 |
1.93 |
?.54 |
2.90 |
3.12 |
3.19 |
3.32 |
3.39 |
3.43 |
|
107.5 |
?3.5 |
0.85 |
1.48 |
1.93 |
2.52 |
2.84 |
3.02 |
3.08 |
3.17 |
3.20 |
3.21 |
|
10?. s |
?0.4 |
0.86 |
1.48 |
1.93 |
2.49 |
2.78 |
2.93 |
2.97 |
3.03 |
3.03 |
3.01 |
|
97.5 |
1 7.6 |
0.86 |
1.47 |
1.90 |
2.43 |
2.69 |
2.81 |
2.83 |
2.85 |
2.8? |
2.76 |
|
9?. 5 |
15.0 |
0.86 |
1.46 |
1.89 |
2.38 |
2.62 |
2.71 |
2.72 |
2.71 |
2.66 |
2.58 |
|
87. S |
12.7 |
0.86 |
1.46 |
1.87 |
2.34 |
2.55 |
2.62 |
2.63 |
?.<9 |
2.5? |
2.43 |
|
8?. 5 |
10.7 |
0.86 |
1.45 |
1.85 |
2.?9 |
2.48 |
2.52 |
2.52 |
2.46 |
?.36 |
2.25 |
|
77.5 |
8.9 |
0.85 |
1.43 |
1.82 |
2.23 |
2.38 |
2.40 |
2.38 |
2.29 |
?.17 |
2.04 |
|
7?. 5 |
7.3 |
0.85 |
1.41 |
1.79 |
?.17 |
2.29 |
2.28 |
2.24 |
2.13 |
1.99 |
1 .85 |
|
67.5 |
5.9 |
0.84 |
1.39 |
1.75 |
2.09 |
2.18 |
2.13 |
2.09 |
1.95 |
1.70 |
1.63 |
|
6?. 5 |
4.7 |
n,84 |
1.38 |
1.72 |
2.03 |
2.09 |
2.03 |
1.98 |
1.82 |
1.64 |
1.48 |
|
57.5 |
3.7 |
0.83 |
1.35 |
1.67 |
1.95 |
1.97 |
1.88 |
1.81 |
1.63 |
1.44 |
1.27 |
|
5?. 5 |
2.8 |
0.82 |
1.33 |
1.63 |
1.86 |
1.85 |
1.73 |
1.66 |
1.46 |
1.2^ |
1.09 |
|
i.7.5 |
2.1 |
0.82 |
1.31 |
1.60 |
1.81 |
1.77 |
1.64 |
1.56 |
1.35 |
1.15 |
0.98 |
|
^?.S |
1.5 |
0.8? |
1.31 |
1.59 |
1.79 |
1.75 |
1.61 |
1.53 |
1.32 |
1.1? |
0.94 |
|
37.5 |
1.0 |
0.82 |
1.31 |
1.59 |
1.78 |
1.74 |
1.60 |
1.52 |
1.31 |
i.n |
0.94 |
|
3?. 5 |
0.7 |
0.82 |
1.31 |
1.59 |
1.78 |
1.74 |
1.60 |
1.52 |
1.31 |
i.n |
0.94 |
are shown in Figure 11. Table 3 and Figures 8, 9, and 11 indicate that if size at recruitment remains constant at 32.5 cm, very little increase in yield per recruit ('^5%) can be expected if effort is increased, and if effort remains constant, very little (~10% ) increase in yield per recruit can be expected by increasing size at reciiiit- ment. However, if fishing effort is doubled (i.e., multiplier = 2.0) and size at recruitment in- creased to 55 cm (3.2 kg), yield per recruit would increase 15% , or if size at recruitment is increased to 77.5 cm (~10 kg), yield per re- cruit would increase about 30% (Table 3). Since the line of eumetric fishing shows that optimum size at recruitment changes with fishing effort, any "minimum size" regulation must be geared to fishing effort.
If fishermen are unable to distinguish the size of yellowfin before capturing them and a mini- mum size regulation prevents their landing, then the discarding of dead yellowfin will occur. Table 4 presents landings per recruit by gear and Figure 12 the landings per recruit for the total fishery when killing and discarding ("dumping") of all yellowfin smaller than the size limit occurs. If the minimum size limit is 55 cm and effort remains the same, then a 2.7% decrease in landings per recruit would occur; and a 13% decrease in landings per recruit would occur if the minimum size is set at 77.5 cm. If effort is doubled and the minimum size is 55 cm, then a 1% increase in landings per recniit would occur; with a minimum size of 77.5 cm, a 16% decline in landings per recruit would
30 4.0 4 5 50 5 5
1,0 1.5 2.0 2.5
MULTIPLIER OF EFFORT
3.0
3.5
Figure 11. — Yield-per-recruit (kg) isopleths for the entire Atlantic yellowfin tuna fishery. Dotted curve is the line of eumetric fishing.
00
0.5 1.0 1.5 2.0 25 3.0
MULTIPLIER OF FISHING EFFORT
Figure 12. — Landings-per-recruit (kg) isopleths for Atlan- tic yellowfin tuna when all fish less than the minimum size that are caught are discarded dead.
49
FISHERY BULLETIN, VOL. 72. NO. 1
Table 4. — Landings per recruit (kg) when M = 0.8, initial F- = 0.2, growth curve of LeGuen and Sakagawa (1973) is used, and yellowfin less than the minimum size are caught and discarded dead.
|
Riir R04TS |
|||||||||||
|
MIMIMIJM |
<:I7E |
MULTIPLIEO OF |
FFFORT |
||||||||
|
CM |
KG |
0.? |
0.4 |
0.6 |
1.0 |
1.4 |
1.8 |
2.0 |
?.5 |
3,0 |
3,5 |
|
laa.s |
Ju.h |
0.07 |
0.1? |
0.15 |
0.18 |
0.18 |
0.17 |
0.16 |
0.14 |
0,12 |
0.10 |
|
117.5 |
30.6 |
0.08 |
0.14 |
0.18 |
0.2? |
0.2? |
0.22 |
0.21 |
0.19 |
0,16 |
0.14 |
|
11?. s |
?6.9 |
0.10 |
0.17 |
0.2? |
0.27 |
0.29 |
0.28 |
0.?8 |
0.?5 |
0,22 |
0.19 |
|
107.5 |
?J.5 |
0.12 |
o.?o |
0.26 |
0..33 |
0.36 |
0.36 |
0.16 |
0.33 |
0,3(1 |
0.?7 |
|
10?. 5 |
?0.i. |
0.14 |
0.24 |
0.31 |
0.40 |
0.44 |
0.45 |
0.44 |
0.42 |
0,39 |
0.35 |
|
97.5 |
W.6 |
0.16 |
0.27 |
0.36 |
0.48 |
0.53 |
0.56 |
0.56 |
0.54 |
0,51 |
0.47 |
|
9?. 5 |
15.0 |
0,18 |