BEACHAM ET AL.: VIKON FilVKR CHUM SALMON POPULATION 



females at all ages examined (P < 0.05) (Table 3). 

 Although there could be significant variation in 

 mean length-at-age among populations (P < 0.05), 

 Yukon River chum salmon were substantially 

 smaller than chum salmon of the same age spawn- 

 ing in British Columbia {P < 0.05). Size differences 

 between Yukon River and British Columbia chum 

 salmon increase with age, with age 3 Yukon River 

 males 94% of the length of age 3 British Columbia 

 males, but age 5 Yukon River males are 86% of the 

 length of their British Columbia counterparts. Sim- 

 ilar results were also observed for females. 



We examined whether there was any differen- 

 tiation of selected morphometric characters with 

 respect to sexual dimorphism or distance of fresh- 

 water migration. With the morphometric measure- 

 ments of both males and females standardized to a 

 postorbital-hypural length of 520 mm, males had 

 longer postorbital head lengths, thicker caudal 

 peduncles, longer base length of the dorsal fin, and 

 longer dorsal and anal fins (all P < 0.05) (Table 4). 

 No sexual dimorphism in base length of the anal fin 



was observed. Significant population differences in 

 the relative sizes of the morphometric characters 

 were also observed, with the Kluane River popula- 

 tion having the relatively smallest characters, and 

 the P'ishing Branch River population having the pro- 

 portionately largest characters. 



Substantial differences exist in length of fresh- 

 water migration between Yukon River fall chum 

 salmon and chum salmon in British Columbia. The 

 relative sizes of the morphometric characters ex- 

 amined are all smaller for Yukon River chum salmon 

 than for chum salmon in British Columbia (Table 4), 

 perhaps illustrating morphometric adaptation of 

 Yukon River chum salmon to the long freshwater 

 migration. 



Developmental Biology 



Fecundity and Egg Size 



The fecundity-length relationship for 14 female 

 chum salmon is described by 



Table 2.— Mean number of gill rakers on left anterior gill arch 

 and mean number of branchiostegal rays on left side for Yukon 

 River fall chum salmon sampled during 1984. Standard error 

 of mean is in parentheses. One hundred fish were sampled 

 per population. Data for 9,206 British Columbia chum salmon 

 are from Beacham and Murray (1987). 



F = 0.100 L 



L60 



where F = number of eggs and L is postorbital- 

 hypural length (mm). Mean fecundity of age 4 

 females was 2,271 eggs (SD = 208, n = 7), and that 

 of age 5 females was 2,451 eggs (SD = 106, n = 3). 

 Mean egg weight of the five Kluane River females 

 used in the study of developmental biology ranged 

 from 145 mg (SD = 6 mg) to 210 mg (SD = 5 mg). 

 Mean diameters ranged from 6.66 mm (SD = 0.21 

 mm) to 7.25 mm (SD = 0.18 mm). Mean egg size 

 of Yukon River chum salmon is substantially smaller 

 than the mean weight of 290 mg and mean diam- 

 eter of 8.39 mm for egg size of chum salmon in 



Table 3. — Mean postorbital-hypural length-at-age (mm) for chum salmon sampled on the spawning grounds during 

 1984-85. Sample sizes are given in parentheses. The mean length-at-age for British Columbia chum salmon was 

 derived from Beacham and Murray (1987). 



667 



