SHAKLEE ET AL.: BIOCHEMICAL GENETICS OF PACIFIC BLUE MARLIN 



expected, the relatively high level of genetic 

 variation reported above for blue marlin is not 

 unique among large marine vertebrates as sev- 

 eral other scombroid fishes (e.g., white marlin, 

 southern bluefin tuna, and Spanish mackerel) ex- 

 hibit similar or even higher levels of variation 

 (Edmunds 1972; Smith and Jamieson 1980; Lew- 

 is 1981; Shaklee unpubl. data). 



The observed pattern of genetic variation can 

 be used to subdivide the 11 variable loci into two 

 general categories. Four loci (Aat, Adh, G-3-Pdh- 

 2, and Iddh) form one group characterized by 

 high heterozygosities (0.4219-0.4944) due to the 

 presence of at least two relatively common alleles. 

 The second group, which is composed of the re- 

 maining seven variable loci (Ada, Gpi-A, Idh-1, 

 Mpi, Pgdh, Pgm, and Umb), is characterized by 

 low heterozygosity per locus (0.0099-0.0896) and 

 the presence of a single common allele at a fre- 

 quency of at least 0.95. In reality, both groups of 

 loci are of utility in population analyses because 

 the power of the statistical tests for detecting sig- 

 nificant differences in allele frequency between 

 pairs of samples actually increases somewhat as 

 the frequencies approach the extremes (i.e., 

 and 1.0) compared with samples having fre- 

 quency distributions close to 0.5. 



The close agreement between observed and ex- 

 pected genotypic frequencies for all but one of 

 the variable loci is consistent with all 95 fish 

 analyzed belonging to a single panmictic popula- 

 tion. However, the significant (P<0.01) defi- 

 ciency of heterozygotes observed at the Adh locus 

 is not. Although this observation may be due to 

 selection or simply be an anomaly, another poten- 

 tial explanation is that this heterozygote defi- 

 ciency is due to the mixing of two or more differ- 

 ent stocks of blue marlin which have different 

 frequencies of the two Adh alleles (Wahlund 

 effect). Such potential stock mixing would not be 

 unreasonable given the presumed migratory na- 

 ture of Pacific blue marlin. 



The fundamental significance of the above ob- 

 served levels of genetic variation is that they are 

 adequate to allow a biochemical genetic analysis 

 of stock structure in Pacific blue marlin. We are 

 now in the process of initiating just such an anal- 

 ysis and are employing an experimental design 

 which should allow us to detect stock heteroge- 

 neity which has either a stable geographical basis 

 or a temporally shifting geographic basis. The 

 former basis for stock heterogeneity, namely the 

 localization of two or more stocks in different re- 

 gions of the species' range is by far the most com- 



monly observed form of population subdivision 

 among organisms. We will be testing for this 

 type of heterogeneity by analyzing samples from 

 different localities (Hawaii, Guam, Samoa, etc.) 

 throughout the range of the Pacific blue marlin. 

 However, this type of analysis is complicated by 

 limited access to marlin caught in many areas of 

 the range, by the shifting patterns of abundance 

 which characterize this species, and by the vir- 

 tual impossibility of obtaining simultaneous sam- 

 ples of blue marlin from multiple localities 

 throughout the range. Indeed, it is the apparent 

 migratory nature of the species which suggests 

 that the second type of population structuring, 

 that based on both temporal and geographic iso- 

 lation, may be occurring in this species. Our ap- 

 proach to this problem is to sample continuously 

 in the Hawaiian Islands to look for significant 

 seasonal shifts in allele frequency such as might 

 be expected if different stocks of blue marlin mi- 

 grate past the Hawaiian Islands at different 

 times of the year. Given the present potentially 

 overfished nature of billfish stocks and the diffi- 

 culties associated with alternative forms of stock 

 analysis such as tag-recapture studies, this bio- 

 chemical genetic approach may well represent 

 the only practical means of gathering informa- 

 tion on stock structure in a time frame compat- 

 ible with the urgent need for the formulation of 

 meaningful management programs for this spe- 

 cies. 



ACKNOWLEDGMENTS 



We wish to gratefully acknowledge the support 

 and encouragement provided by the staff and 

 Board of Governors of the Hawaiian Interna- 

 tional Billfish Association and the cooperation 

 of all the participants in the 1980 Hawaiian In- 

 ternational Billfish Tournament. The valuable 

 help provided by Jerry Kinney and his staff at 

 the Volcano Isle Fish Co. is also sincerely appre- 

 ciated. 



LITERATURE CITED 



Allendorf, F. W.. and F. M. Utter. 



1979. Population genetics. InW. S Hoar, D. J. Randall, 

 and J. R. Brett (editors). Fish physiology, Vol. 8, p. 407- 

 454. Academic Press, Inc., N.Y. 

 Ayala, F. J. (editor). 



1976. Molecular evolution. Sinauer Assoc, Inc., Sun- 

 derland, Mass., 277 p. 

 Berst, A. H.. and R. C. Simon. 



1981. Introduction to the Proceedings of the 1980 Stock 

 Concept International Symposium (STOCS). Can. J. 



89 



