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Fishery Bulletin 101(2) 



50°- 



Figure 1 



Locations in the Fraser River drainage where chinook salmon spawning aggregates were 

 sampled at least once during 1988-98, as well as locations of the commercial and test fisher- 

 ies in the lower river and commercial fishery in the mid Fraser 



1999). The probabilities of individuals belonging to all pop- 

 ulations were calculated by using a Bayesian approach and 

 each individual was assigned to the population in which it 

 had the highest marginal probability. 



Estimation of stock composition 



Genotypic frequencies were determined at each locus in 

 each population and the statistical package for the analysis 

 of mixtures software program (SPAM) (Dcbevec et al., 2000) 

 was used to estimate stock composition of each mixture. 

 More alleles were present at the microsatellite loci than was 

 practical for stock identification applications. We combined 



low frequency (frequency generally <0.02 in all populations) 

 adjacent alleles to reduce the number of genotypic frequen- 

 cies to be estimated with the available samples with the 

 pooling strategy for each locus outlined in Table 2. This was 

 done to minimize and hopefully eliminate the occurrence of 

 fish in the mixed sample from a specific population having 

 an allele not observed in the baseline samples. Expected 

 genotypic frequencies under Hardy- Weinberg equilibrium 

 were determined from the observed allele frequencies and 

 were used as model inputs. Genotypic frequencies at Otsl02 

 were not in Hardy-Weinberg equilibrium in approximately 

 50% of the populations surveyed (Beacham et al., 2003), 

 but increased accuracy in estimated stock compositions was 



