BIOCHEMICAL GENETICS OF PACIFIC BLUE MARLIN, 

 MAKAIRA NIGRICANS, FROM HAWAIIAN WATERS 1 



James B. Shaklee, 2 Richard W. Brill, 3 and Robin Acerra 4 



ABSTRACT 



An electrophoretic survey of 35 enzyme-coding gene loci in Pacific blue marlin was accomplished 

 to determine levels of genetic variation and the feasibility of using electrophoresis to study stock 

 structure in this species. Polymorphism (P99) in the marlin was 0.26 and the average heterozygosity 

 (H) was 0.06. Allele frequencies at 11 variable loci were determined for a sample of 95 fish from 

 Kona, Hawaii. The observed levels of polymorphism and heterozygosity suggest that a biochemical 

 genetic analysis of blue marlin stock structure is possible and may reveal stock heterogeneity. 



The Pacific blue marlin, Makaira nigricans, is 

 the predominant billfish species in the central 

 tropical Pacific. As such, it is an important com- 

 mercial species and the object of a considerable 

 sport fishery. The average annual catch of this 

 species in the Pacific exceeds 14,000 t (metric 

 tons) (Shomura 1980). The Pacific blue marlin is 

 primarily distributed in equatorial areas, al- 

 though Japanese longliner catch records indi- 

 cate that its range extends from lat. 48°N to 

 48°S. During the Southern Hemisphere summer 

 (December through March) a center of concen- 

 tration occurs in the western and central South 

 Pacific (between lat. 8°S and 26°S). In the North- 

 ern Hemisphere summer (May through October) 

 a center of concentration occurs in the central 

 North Pacific (between lat. 2°N and 24 °N). Dur- 

 ing April and November the fish appear to be 

 concentrated equatorially between lat. 10°N and 

 10°S (Rivas 1975). There is currently no direct 

 evidence of migration of blue marlin within the 

 Pacific. However, a general movement to the 

 northwestern Pacific during the Northern Hem- 

 isphere summer and to the southeastern Pacific 

 during the Southern Hemisphere summer has 

 been postulated by Howard and Ueyanagi (1965) 



'Contribution No. 652 from the Hawaii Institute of Marine 

 Biology. 



2 Hawaii Institute of Marine Biology and Department of Zool- 

 ogy, University of Hawaii, Honolulu, Hawaii; present address: 

 Division of Fisheries Research, CSIRO Marine Laboratories, 

 233 Middle Street, Cleveland, Queensland 4163, Australia. 



:i Pacific Gamefish Foundation, Honolulu, Hawaii; present 

 address: Southwest Fisheries Center Honolulu Laboratory, 

 National Marine Fisheries Service, NOAA, P.O. Box 3830. 

 Honolulu, HI 96812. 



4 Hawaii Institute of Marine Biology, University of Hawaii. 

 Honolulu, Hawaii; present address: Southampton College, 

 Long Island University, Southampton, NY 11968. 



on the basis of the shifting abundance patterns of 

 the fish. 



Little is known about spawning, other than that 

 Pacific blue marlin appear to spawn throughout 

 the year in an area 10°-20° on either side of the 

 Equator, and up to 30° on either side of the E qua- 

 tor during the Northern and Southern Hemis- 

 pheres' respective summer months. In general, 

 the highest spawning densities occur in the west- 

 ern Pacific, with the density decreasing eastward 

 (Strasburg 1970; Matsumoto and Kazama 1974; 

 Rivas 1975). Because of the apparently single 

 equatorial Pacific spawning area, it has been as- 

 sumed that the species consists of a single unit 

 stock (Yuen and Miyake 1980; Yoshida 1981), yet 

 there has been no direct test of this assumed 

 stock structure. The most recent report available 

 on the condition of the Pacific blue marlin stock 

 considers it to be badly overfished. Yuen and 

 Miyake ( 1980) calculated that the present fishing 

 effort (commercial longliner effort only, since no 

 data are available on recreational fishing effort) 

 is about twice that suitable for maximum sus- 

 tainable yield. Because the catch per unit effort 

 of Pacific blue marlin has steadily declined over 

 the past 10 yr, in spite of a fairly constant level 

 of effort, Yuen and Miyake (1980:19) concluded 

 "...that continued fishing at high levels will con- 

 tinue to reduce the abundance of the stock and a 

 recruitment failure will become a distinct possi- 

 bility." 



The importance of being able to define sub- 

 populations or stocks of fishes with respect to the 

 formulation of appropriate fishery management 

 schemes has long been recognized (Marr 1957). 

 This problem is especially acute for species (such 

 as Pacific blue marlin) which are highly migra- 



Manuscript accepted June 1982. 



FISHERY BULLETIN: VOL. 81. NO. 1, 1983. 



85 



