776 



Fishery Bulletin 101(4) 



als that originated in discrete spawning grounds, should be 

 undertaken to prove the presence of an independent unit 

 inside the Gulf of California, which, if confirmed, might 

 necessitate new stock management strategies. 



Allele frequencies for Gpi-F* locus found in the present 

 study, apparently, correspond to those reported by Ward et 

 al. (1994 and 1997). These authors reported a higher pro- 

 portion of the allele Gpi-F*75 (0.571) in the eastern Pacific 

 region and a gradual decrement of the same allele toward 

 the central (0.423) and western Pacific regions (0.330), 

 where allele Gpi-F*100 (0.650) had the higher proportion. 

 In the present study, the highest frequencies for the allele 

 Gpi-F*75 corresponded to the region of the eastern Pacific, 

 situated in the limits of the yellowfin tuna regulatory area 

 (offshore region), and there was a slight decrease in fre- 

 quencies towards the coastal area (Table 5). Furthermore, 

 allele frequencies for the Gpi-F*75 allele from the coastal 

 locality, Colima (0.444), and the intermediate locality 

 southeast, Clipperton Islands (0.409), have coincidences 

 with those reported by Ward et al. ( 1994) for the collection 

 Hawaii 92 (0.423) in the central Pacific region. 



The similarities in the Gpi-F* allelic frequencies be- 

 tween eastern (Colima and Clipperton) and central Pacific 

 samples (Hawaii 92) might possibly be attributed to the 

 extended migrations of yellowfin tuna in the eastern Pa- 

 cific brought about by the strong influence of warm waters 

 on tuna movements because of the increased depth of the 

 thermocline layer in that area, which was reflected by a 

 decrease in catches (Joseph and Miller, 1988; Wild, 1994) 

 and which possibly led to the mixing of the eastern and 

 central Pacific stocks. 



The low number of RAPD loci analyzed and the uncer- 

 tainty of fulfilling some assumptions, such as the genetic 

 identity of each band needed for qualitative and quantita- 

 tive interpretation of data in terms of allelic frequencies, 

 do not allow us to consider our estimations of subdivision 

 reliable with the RAPD method. Additionally, the lack of 

 reliability of estimations associated with high sampling 

 variances by using randomly collected fishery samples 

 highlights the need to design more efficient spatial and 

 temporal sampling strategies in local and wide areas, as 

 well as the need for alternative hypervariable markers to 

 assess the divergence patterns observed in highly migra- 

 tory species. 



Acknowledgments 



We are grateful to Ernesto Escobar from Pescados Industri- 

 alizados S. A. PINSA for allowing the sampling, and Robert 

 Olson from lATTC for providing the Gulf of California 

 samples. We thank Monica Dominguez-Lopez, Yolanda 

 Hornelas-Orozco, Evangelina Castillo, and Alma Hernan- 

 dez-Perez, for collection and processing of samples, Luis 

 Eguiarte and Valeria Souza for the facilities provided in 

 their laboratory and three anonymous reviewers for their 

 valuable comments. This manuscript benefited from the 

 critical reading of John Graves, Jan McDowell, and Bar- 

 bara Rutan. Funding for this project was provided by the 

 Programa de Apoyo a Estudiantes de Posgrado (PADEP) 



and by the project IN20598 of the Programa de Apoyo 

 a Proyectos de Investigacion e Innovacion Tecnologica. 

 Direccion General de Asuntos del Personal Academico, 

 Universidad Nacional Autonoma de Mexico. 



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