234 



Fishery Bulletin 101(2) 



Population structure 



The mean F^.^ value over 52 samples and 13 loci surveyed 

 was 0.039 (0.040 with Otsl02 excluded), and the dinucleo- 

 tide loci had higher mean Fgy. values (0.067) than the other 

 loci (mean=0.026) (Table 2). With the exception of several 

 sampling locations within tributaries affected by trans- 

 plantation (discussed below), the geographically distinct 

 sampling sites of this study possessed individual spawning 

 populations of chinook salmon. Neighbor-joining cluster- 

 ing based on F^-j. values for the 12 loci in HWE indicated a 

 regional population structure which corresponded broadly 

 to six groups: lower, middle, and upper Fraser River, and 

 south, north, and lower Thompson River. An exception 

 was the Birkenhead River population of the lower Fraser 

 region, which was distinct from all other populations 

 (Fig. 2). Thompson River populations were well differ- 

 entiated from those of the Fraser River, and within the 

 Thompson River drainage, the populations of the south, 

 north, and lower regions were distinctive. Only the Louis 



Creek population of the north Thompson failed to cluster 

 geographically, instead grouping rather distantly with the 

 lower Thompson populations. The mid and upper Fraser 

 River populations each formed distinctive gi'oups, although 

 the Portage Creek and Bridge River populations of the 

 mid Fraser showed similarities to lower Fraser and lower 

 Thompson populations, respectively. The transplanted red- 

 fleshed "Chilliwack" and "Chehalis" River populations in 

 the lower Fraser drainage clustered with source popula- 

 tions Slim Creek and Bowron River from the upper Fraser 

 drainage. Mean F,,.^. values both within and among regions 

 were statistically significant (all P<0.05) (Table 3). 



The distinctive lower Fraser region, providing the Har- 

 rison and Chilliwack River samples, was differentiated 

 from all other regions, although F,,, values indicated a 

 somewhat closer relationship of lower Fraser with mid 

 Fraser populations than with populations of other regions 

 (Table 3). The distinctiveness of the Birkenhead River 

 population was apparent in the F^.j. values obtained in 

 comparisons with all regional groups. The upper Fraser 



