SHARP and FRANCIS: ENERGETICS MODEL FOR YELLOWFIN TUNA POPULATION 



over highly productive regions where their main 

 sources of competition are probably porpoise 

 and bigeye tuna, Thunnus obesus. The porpoise- 

 tuna composite likely indicates the optimum 

 availability offish and squid in the eastern tropi- 

 cal Pacific. It is obvious from the Perrin et al. 

 (1973) studies that the two Stenella species and 

 tunas coexist but tend to feed differentially. 

 The tuna diet shares most of the organisms 

 found in both species indicating that they are 

 less selective and/or feed throughout the water 

 column. 



No data support the concept of food limitation 

 for population size in yellowfin tuna in post- 

 recruit sizes and in most cases the arguments 

 tend toward the opposite conclusion. Since no 

 stable relationship can be found to exist be- 

 tween recruitment and spawning biomass, it is 

 unlikely that reproductive success is affected by 

 spawning biomass at the population levels we are 

 experiencing. More probable is that the environ- 

 mental parameters are more important in regulat- 

 ing the absolute numbers of surviving larval or 

 juvenile yellowfin tuna which are recruited to 

 the fishery. 



In the future, we plan to incorporate the avail- 

 able productivity and environmental data (tem- 

 perature, oxygen, etc.) with a more complete 

 version of this model. We hope to determine the 

 environmental correlates with the fluctuations in 

 the catch, effort, and length-frequency data 

 generated from the fishery on yellowfin tuna. Pre- 

 liminary studies have been encouraging (Inter- 

 American Tropical Tuna Commission 1975) and 

 point up the need for data on the thermal pref- 

 erences (perhaps indicating energetic optima) 

 and the levels of environmental variability which 

 can be sensed and therefore compensated for by 

 the several tuna species at the various develop- 

 mental stages in their life cycles. Also obvious is 

 the need to work with smaller areas and corre- 

 sponding population segments rather than as- 

 suming "average" conditions in environmental 

 and population parameters. The ultimate goal of 

 these studies is the development of predictive 

 tools for use in assessing likely catch conditions 

 as well as the basic distributional properties of 

 the tunas. The use of unsupported guesses based 

 on overviews which integrate vast areas with sig- 

 nificant oceanographic and population structure 

 differences may do little more than obscure the 

 existing relationships which are important to 

 this goal. The application of the crude model we 



have described in this study will depend upon 

 the development of better estimates of the 

 physiological parameters and appropriate use 

 of the areal breakdown in the population simu- 

 lator. Studies of trophic dynamics and competi- 

 tion interactions would help complete the pic- 

 ture necessary to "efficiently" manage a dynamic 

 resource. We hope to generalize, where possible, 

 the relationships which arise fi-om these analyses 

 in order to provide a useful descriptive tool as 

 well as a hypothesis testing device for studying 

 the occurrence, abundance, and availability of 

 tunas in the world ocean. 



LITERATURE CITED 



Alverson, F. G. 



1963. The food of yellowfin and skipjack tunas in the 

 eastern tropical Pacific Ocean. [In Engl, and Span.] 

 Inter-Am. Trop. Tuna Comm. Bull. 7:293-396. 

 BAINBRIDGE, R. 



1961. Problems of fish locomotion. Symp. Zool. Soc. 

 Lond. 5:13-32. 

 BLACKBURN, M., R. M. LAURS, R. W. OWEN, AND B. 

 ZEITZSCHEL. 



1970. Seasonal and areal changes in standing stocks of 

 phytoplankton, zooplankton and micronekton in the 

 eastern tropical Pacific. Mar. Biol. (Berl.) 7:14-31. 



Carey, F. G., and J. M. Teal. 



1966. Heat conservation in tuna fish muscle. Zoology 

 56:1464-1469. 

 CHATWIN, B. M. 



1959. The relationships between length and weight of 

 yellowfin tuna (Neothunnus macropterus) and skipjack 

 tuna (Katsuwonus pelamis) fi-om the Eastern Tropical 

 Pacific Ocean. [In Engl, and Span.] Inter-Am. Trop. 

 Tuna Comm. Bull. 3:305-352. 



farris, d. a. 



1961. Abundance and distribution of eggs and larvae 

 and survival of larvae of jack mackerel (Trachurus sym- 

 metricus). U.S. Fish Wildl. Serv., Fish. Bull. 61:247-279. 

 Francis, R. C. 



1974. TUNP0P, a computer simulation model of the 

 yellowfin tuna population and the surface tuna fishery 

 of the eastern Pacific Ocean. [In Engl, and Span.] 

 Inter-Am. Trop. Tuna Comm. Bull. 16:235-279. 



FRY, F. E. J. 



1957. The aquatic respiration of fish. In M. E. Brown 

 (editor), The physiology of fishes, Vol. 1, p. 1-63. Aca- 

 demic Press Inc., N.Y. 

 Gooding, R., E. Poe, and C. Nagamine. 



1973. Tuna newsletter No. 9 July 1973. Natl. Mar. Fish. 

 Serv., Southwest Fisheries Center, La Jolla, Calif 



hennemuth, r. c. 



1961. Size and year class composition of catch, age and 

 growth of yellowfin tuna in the eastern tropical Pacific 

 Ocean for the years 1954-1958. [In Engl, and Span.] 

 Inter-Am. Trop. Tuna Comm. Bull. 5:1-112. 



Inter-American Tropical Tuna commission. 



1975. Aimual Report of the Inter-American Tropical Tuna 

 Commission, 1974. [in Engl, and Span.] 169 p. 



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