769 



Abstract— Stock structure of eastern 

 Pacific yellowfin tuna was investigated 

 by analyzing allozymes and random 

 amplified polymorphic DNAs (RAPDs) 

 from 10 samples of 20-30 individu- 

 als each, collected between 1994 and 

 1996 from fishing vessels operating 

 in the Inter-American Tropical Tuna 

 Commission (lATTC) yellowfin regula- 

 tory area (CYRA). Allozyme analysis 

 resolved 28 loci, eight of which were 

 polymorphic under the 0.95 criterion: 

 Aat-S*. Gtucl. GpiF*, Gpi-S*, La, Lgg, 

 PapF*, and 6-Pgd, resulting in a mean 

 heterozygosity over all allozyme loci of 

 H = 0.052. Four polymorphic RAPD loci 

 were selected for analysis, resulting 

 in a mean heterozygosity of H = 0.43. 

 Eight of 45 pairwise comparisons of 

 allozyme allele frequencies among the 

 ten samples showed significant differ- 

 ences after correction for multiple test- 

 ing (P<0.0001), all of which involved 

 comparisons with the Gulf of California 

 sample. Confirmation of this signal of 

 population structure would have man- 

 agement implications. No significant 

 divergence in RAPD allele frequencies 

 was observed among samples. Weir and 

 Cockerham 9 estimated for allozyme 

 loci (6=0.048; P<0.05) and RAPD loci 

 (6=0.030; P>0.05) revealed little popu- 

 lation structure among samples. Mantel 

 tests demonstrated that the genetic 

 relationships among samples did not 

 correspond to an isolation-by-distance 

 model for either class of marker. Four 

 of eight comparisons of coastal and 

 offshore samples revealed differences 

 of allele frequencies at the Gpi-F* locus 

 (P<0.05), although none of these differ- 

 ences was significant after correction 

 for multiple testing (P>0.001). Results 

 are consistent with the hypothesis that 

 the CYRA yellowfin tuna samples com- 

 prise a single genetic stock, although 

 gene flow appears to be greater among 

 coastal samples than between coastal 

 and offshore samples. 



Allozyme and RAPD variation in the eastern 

 Pacific yellowfin tuna Whunnus albacares) 



Pindaro Dfaz-Jaimes 



Instituto de Ciencias del Mar y Limnologia 



Unlversidad Nacional Autonoma de Mexico 



Circuito exterior de Ciudad Universitaria 



Apdo. Postal 70-305 



Mexico, D F 04510 



E-mail address; pindaro@maricmyl-unam.mx 



Manuel Uribe-Alcocer 



Instituto de Ciencias del Mar y Limnologia 

 Universidad Nacional Autonoma de Mexico 

 Circuito exterior de Ciudad Universitaria 

 Apdo, Postal 70 305 

 Mexico, D.F 04510 



Manuscript approved for publication 

 19 June 2003 by Scientific Editor 



Manuscript received 26 June 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. 101:769-777. 



Yellowfin tuna (Thunnus albacares) is a 

 cosmopolitan species inhabiting tropical 

 and subtropical waters in the Atlantic, 

 Pacific, and Indian oceans. This species 

 has accounted for more than a third of 

 the world's tuna production since 1970. 

 The eastern Pacific has contributed 

 from 21% to 26% of the global catch 

 from 1993 through 1997, represent- 

 ing 273,329 metric tons (t) in 1990 to 

 264,426 t in 1998 (lATTC, 1999). 



Yellowfin tuna is a large pelagic fish 

 with a common size of 150 cm (Collette 

 and Nauen, 1983). Spawning occurs 

 throughout the year in the tropical 

 oceans, preferably near islands and 

 coasts (Leis et al., 1991). Growth is 

 rapid and individuals reach maturity 

 by the end of the second year (Suzuki 

 et al., 1978). Schooling of individuals 

 of similar size is observed near surface 

 waters and is often associated with 

 floating objects (Wild, 1994). 



Yellowfin tuna is currently consid- 

 ered to comprise a single species (Gibbs 

 and CoUete, 1967), although significant 

 morphometric and meristic differences, 

 limited fish movements, and differences 

 among catch data, have been reported 

 for the different regions of the Pacific 

 Ocean (Godsil and Greenhood, 1951; 

 Schaefer, 1955; Joseph et al., 1964; 

 Suzuki et al., 1978; Schaefer, 1991). 

 Population structure in yellowfin tuna 

 has been addressed in the Pacific Ocean 

 by using several independent methods. 



Morphometric and meristic based stud- 

 ies have shown significant differences 

 (Godsil and Greenhood, 1951; Schaefer, 

 1955; Kurogane and Hiyama, 1957), 

 and at least three stocks or discrete 

 units (western, central, and eastern Pa- 

 cific) have been proposed. More recent 

 studies using morphometric multivari- 

 ate analysis suggest the presence of dif- 

 ferent stocks between north and south 

 regions in the eastern Pacific (Schaefer, 

 1991), as well as across the Pacific 

 Ocean (Schaefer, 1991). Additionally, 

 differences in larval distribution, catch 

 rates, and size composition data of yel- 

 lowfin tuna caught along the equatorial 

 Pacific by longline and purse-seine have 

 been used by Suzuki et al. ( 1978) to dis- 

 tinguish between western, central, and 

 eastern Pacific groups. 



Tagging experiments have shown 

 limited movement of yellowfin tuna 

 between western and eastern Pacific 

 waters (Joseph et al., 1964; Fink and 

 Bayliff, 1970). In the eastern Pacific, 

 the presence of two groups has been 

 suggested: a northern group off Baja 

 California coast and the Revillagigedo 

 Islands and a southern group from the 

 Maria Islands through Chile. Some 

 mixing occurs between them (Fink 

 and Bayliff, 1970). There seem to be 

 marked movements between north 

 and south groups along the coast with 

 limited westward movements (Joseph 

 et al., 1964). 



