296 



Fishery Bulletin 89(2). 1991 



separation of fish from Mexico and Ecuador. The gill- 

 raker counts reported by Godsil and Byers (1944) are 

 based upon relatively few fish from several widely 

 scattered locations in the Pacific, but show differ- 

 ences between fish from Japan and those from Hawaii, 

 Ecuador, and northern Mexico. Differences in the gill- 

 raker counts of fish from Central America and from 

 Hawaii have been reported by Schaefer (1955). > 



I recommend the use of gill-raker counts for sep- 

 aration on a broad geographic scale. However, this 

 character alone is not adequate for the discrimination 

 and classification of individuals from selected geo- 

 graphical locations, and should thus be collected in 

 conjunction with morphometric data to allow finer 

 resolution within major oceanic areas. Because 11 of 

 the 12 adjusted morphometric characters contributed 

 significantly to the stepwise discriminant analysis 

 (Table 4), and because none of the 13 characters 

 (Fig. 2) are potentially difficult to measure, I con- 

 sider the set of 13 characters utilized in this study 

 to be appropriate for future investigations of tuna 

 morphometries. 



Extensive tagging studies designed to investigate 

 movements of yellowfin tuna have been conducted only 

 in the eastern Pacific (Joseph et al. 1964, Bayliff 1979, 

 Hunter et al. 1986). Movements of yellowfin tuna in 

 the eastern Pacific tend to be restricted, with few in- 

 dividuals moving more than several hundred miles. 

 Tagging of yellowfin tuna during 1968-74 in the 

 eastern Pacific, in inshore and offshore areas, indicated 

 few long-distance east-west or north-south movements 

 of the fish. The results of the present study and that 

 of Schaefer (1989) on morphometries of yellowfin tuna 

 in the eastern Pacific also suggest that movements are 

 restricted. The results of this investigation appear to 

 be in reasonably good agreement with those of tagging 

 studies, although several tagged yellowfin tuna re- 

 leased in the central Pacific have been recaptured in 

 the eastern Pacific, and a tagged yellowfin tuna re- 

 leased in the western Pacific was recaptured in the 

 eastern Pacific after traveling a net distance of 3806 

 miles (Peterson 1983). 



Observed morphometric and meristic differences in 

 this investigation are probably influenced both by genes 

 and environment. It would be valuable to conduct a 

 study of the population structure of yellowfin tuna 

 throughout the Pacific; morphometric and meristic data 

 should be collected, along with tissue samples to be 

 analyzed for genetic information. Both mitochondrial 

 DNA and nuclear genes should be screened and ana- 

 lyzed (Avise 1987). This approach would address the 

 genetic basis of the groups inferred from morphometric 

 and meristic differences. The accumulated information 

 from morphometries, meristics, and genetics, along 

 with other life-history information, could then be 



evaluated for a better understanding of the population 

 structure of yellowfin tuna in the Pacific Ocean. 



Acknowledgments 



I would like to thank the following individuals who were 

 of considerable assistance with this investigation: 

 H. Fushimi, C. Heberer, K. Holland, R. Kearney, 

 S. Kume, S. Loomis, F. LoPreste, Z. Suzuki, and 

 B. Takenaka. I am grateful to J. Diplock for collecting 

 the data from Australia. I especially wish to thank the 

 Commission's Director, J. Joseph, for his support 

 throughout this investigation. I thank W. Bayliff, 

 R. Deriso, R. Punsly, and P. Tomlinson, of the Com- 

 mission's staff, for their comments on the manuscript. 

 I extend special thanks to an anonymous reviewer for 

 many useful suggestions. 



Citations 



Avise, J.C. 



1987 Identification and interpretation of mitochondrial DNA 

 stocks in marine species. In Kumpf, H.E., R.N. Vaught, C.B. 

 Grimes, A.G. Johnson, and E.L. Nakamura (eds.), Proceedings 

 of the stock identification workshop, p. 105-136. NOAA Tech. 

 Memo. NMFS-SEFC-199, Southeast Fish. Sci. Cent., Natl. 

 Mar. Fish. Serv., Miami, FL. 

 Bayliff, W.H. 



1979 Migrations of yellowfin tuna in the eastern Pacific Ocean 

 as determined from tagging experiments initiated during 

 1968-1974. Inter-Am. Trop. Tuna Comm. Bull. 17:445-506. 

 Claytor, R.R., and H.R. MacCrimmon 



1986 Partitioning size from morphometric data: A comparison 

 of five statistical procedures used in fisheries stock identifica- 

 tion research. Can. Tech. Rep. Fish. Aquat. Sci. 1531, 31 p. 

 Collette, B.B., and C.E. Nauen 



1983 FAO species catalogue. Vol. 2. Scombrids of the world. 

 FAO Fish. Synop. 125, vol. 2, 137 p. 

 Cook, R.D., and S. Weisburg 



1982 Residuals and influence in regression. Chapman and 

 Hall, NY, 230 p. 

 Dixon, W.J., M.B. Brown, L. Engleman, J.W. Frane, M.A. Hill, 

 R.I. Jenarich, and J.D. Toporek 



1981 BMDP statistical software. Univ. Calif. Press, Berkeley, 

 725 p. 

 Godsil, H.C. 



1948 A preliminary population study of the yellowfin tuna and 

 the albacore. Calif. Dep. Fish Game, Fish Bull. 70, 90 p. 

 Godsil, H.C, and R.D. Byers 



1944 A systematic study of the Pacific tunas. Calif. Dep. Fish 

 Game, Fish Bull. 60, 131 p. 

 Godsil, H.C, and E.E. Greenhood 



1951 A comparison of the populations of the yellowfin tuna, 

 Neothunnus maeropterus, from the eastern and central 

 Pacific. Calif. Dep. Fish Game, Fish Bull. 82, 33 p. 

 Gould, S.J. 



1966 Allometry and size in ontogeny and phylogeny. Biol. 

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