774 



Fishery Bulletin 101(4) 



Table 3 



Estimates of population subdivision 9 (Weir and Cocker- 

 ham, 1984) for allozymes of Thunnus albacares partitioned 

 into longitudinal regions 0^ (regions) (i.e. coastal-interme- 

 diate-offshore) and samples 9^ (overall), n.v. = negative 

 values. P = probability of significance of subdivision esti- 

 mations. Significance of single-locus values was corrected 

 with an initial level of 0.006 (0.05/8 loci). Means and stan- 

 dard error were obtained by the jackknife method. Con- 

 fidence intervals obtained by 1000 resamplings through 

 bootstrapping are also shown. * = signifcant values after 

 Bonferroni correction. 



Locus 



L (regions) 



"O(overall) 



Aat-2* 



Glud 



Gpil* 



Gpi-2* 



La 



Lgg 



Pap-1* 



6-Pgd 



Mean 



CI 95% 



0.0152 



0.0009 



0.0058 



0.0014 

 n.v. 



0.0073 

 n.v. 



0.044 

 0.0067 ±0.0042 

 0.0003-0.0199 



0.072 

 0.227 

 0.086 

 0.780 

 0.012 

 0.004 

 0.068 

 >0.006* 



0.029 



0.086 



0.003 



0.0037 



0.13 



0.27 



0.024 



0.02 

 0.048 ±0.022 

 0.019-0.101 



0.007 

 >0.006* 



0.210 



0.007 

 >0.006* 

 >0.006 



0.001 

 >0.006* 



were polymorphic for all samples (Table 1). No significant 

 heterogeneity of RAPD allele frequencies was found for any 

 locus between any paired sample comparison, among all 

 collections, nor among latitudinal or longitudinal regions 

 (P=0.4806). 



The mean lvalue for all fragments and samples (over- 

 all), as well as regional estimations derived from liAPDs 

 (0.0302), were not significantly different from zero and 

 displayed some negative values. Klstimations of gene 

 flow between sample pairs (Mg) from RAPU data aver- 



Table 4 



Pairwise-regions comparison of allele frequencies for 

 Thunnus albacares. Probabilities of nonheterogeneity for 

 allozymes (based on exact tests) are above the diagonal 

 ( — ) and RAPDs are below the diagonal ( — ). * = significant 

 after corrected for multiple tests (Rice, 1989). 



Region 



Coastal 



Intermediate 



Offshore 



Coastal 



Intermediate 



Offshore 



0.9998 

 0.9039 



0,0632 



0.9126 



0.0043* 

 0.5384 



aged 29.2 migrants per generation. The evaluation of the 

 relationships between geographic distances and the gene 

 flow estimations in pairwise collections (Afg), through the 

 Mantel test, showed a nonsignificant correlation (r-=0.413, 

 P=0.984). 



Discussion 



The test of conformance to the Hardy-Weinberg frequen- 

 cies showed significant differences in Lgg and Pap-F* loci 

 only in the Gulf of California sample, where polymorphism 

 at those loci was also consistently found. Similar results 

 were obtained, with smaller differences in locus Aat-S* 

 from the west of the Revillagigedo Islands and the Gulf of 

 California samples. Considering the fact that our samples 

 were provided by the commercial fleet, they could have 

 included representatives of different schools with differ- 

 ences in genotypic distributions originated by differences 

 in age classes or sexual ratios (or for both) among schools 

 because recruitment of individuals into new schools has 

 been reported to be mainly by aggregating individuals of 



