AGE, MORPHOLOGY, DEVELOPMENTAL BIOLOGY, AND 



BIOCHEMICAL GENETIC VARIATION OF YUKON RIVER FALL 



CHUM SALMON, ONCORHYNCHUS KETA, AND COMPARISONS WITH 



BRITISH COLUMBIA POPULATIONS 



Terry D. Beacham, Clyde B. Murray, and Ruth E. Withler^ 



ABSTRACT 



Fall chum salmon, Oncorhynchtis keta, populations spawning in the Yukon River drainage were surveyed 

 for variation in age, size and shape at maturity, developmental biology, and biochemical genetics. Yukon 

 River fall chum salmon matured at older ages and smaller sizes than chum salmon in British Columbia. 

 They also had proportionately smaller heads, thinner caudal peduncles, and smaller fins than British 

 Columbia chum salmon, perhaps illustrating morphometric adaptation to long distance freshwater migra- 

 tion. Yukon River chum salmon were less fecund and had smaller eggs than those in British Columbia, 

 and they also tended to have faster development to alevin hatching and fry emergence than most British 

 Columbia populations. Maximum alevin and fry size of Yukon River salmon occur at lower water 

 temperatures during development than for most British Columbia populations, possibly indicating a 

 developmental adaptation to low winter water temperatures. Genetic differentiation among chum salmon 

 populations in the Yukon River drainage was observed. 



The Yukon River is a major North American river, 

 originating in British Columbia and flowing over 

 3,200 km through the Yukon Territory and Alaska 

 to the Bering Sea, and draining an area of approx- 

 imately 860,000 km". Five species of Pacific salmon 

 (Oncorhynchus) occur in the Yukon River (Gilbert 

 1922), but chinook, 0. tshawytscha, and chum 

 salmon, 0. keta, are the most abundant and are ex- 

 ploited in commercial and subsistence fisheries 

 (McBride et al. 1983). Chum salmon in the Yukon 

 River are characterized by distinct seasonal races 

 (Gilbert 1922). The early-maturing or "summer" 

 chum salmon return to the Yukon River between 

 early June and mid-July and spawn in the lower 800 

 km of the drainage (Buklis 1981). Later-maturing 

 or "fall" chum salmon enter the Yukon River from 

 mid-July through late August and spawn in the 

 up-river portions of the drainage, migrating as far 

 as 2,800 km upstream (Milligan et al. 1986). Fall 

 chum salmon are also larger than summer chum 

 salmon (Buklis 1981; Buklis and Barton 1984), and 

 generally have higher fecundity and younger age 

 compositions than summer chum salmon (Sano 

 1966). 



'Department of Fisheries and Oceans, Biological Sciences 

 Branch, Pacific Biological Station, Nanaimo, British Columbia, 

 Canada V9R 5K6. 



Chum salmon generally spawn in rivers only a 

 short distance from salt water (<200 km), a trait 

 very different from the long distance freshwater 

 migrations of Yukon River fall chum salmon. Yukon 

 River fall chum salmon are noted for their high oil 

 content upon entering the river (Gilbert 1922), an 

 adaptation necessary to provide sufficient energy 

 reserves for the freshwater migration, as in Amur 

 River chum salmon in the Soviet Union (Nikol'skii 

 1961). Adaptations in other biological characters 

 may reflect the environmental conditions experi- 

 enced by Yukon River fall chum salmon. Thus we 

 examined the variation in life history traits of Yukon 

 River fall chum salmon, and compared this varia- 

 tion to that found in chum salmon in British 

 Columbia. 



In 1984, we began a survey of variation in bio- 

 logical characters of fall chum salmon in the Yukon 

 River. Regional biochemical genetic variation had 

 previously been reported for chum salmon in British 

 Columbia (Beacham et al. 1987), and we investigated 

 the biochemical genetic differentiation of Yukon 

 River fall chum salmon. We had previously exam- 

 ined the adaptive nature of the variation in some 

 morphometric and life history traits of chum salmon 

 in British Columbia (Beacham and Murray 1987) and 

 used this for comparison for Yukon River fall chum 

 salmon. 



Manuscript accepted July 1988. 



FISHERY BULLETIN; VOL. 86, NO. 4, 1988. 



663 



