POPULATION BIOLOGY OF CHUM SALMON, ONCORHYNCHUS KETA, 

 FROM THE FRASER RIVER, BRITISH COLUMBIA 



Terry D. Beacham 1 and Paul Starr 2 



ABSTRACT 



Population biology of Fraser River chum salmon, Oncorhynchus keta, was investigated. Mean age 

 of chum salmon during the run declined from 3.98 years in October to 3.78 years in December in the 

 1970s. Females were more abundant than males in 4-year-old chum salmon, but males were more 

 abundant than females in 3- and 5-year-old chum salmon. Fecundity of females was 3,250 eggs/ 

 female at a standard length of 58.0 cm and did not vary among years sampled. Fry tended to mi- 

 grate downstream earlier when the previous winter had been warm than when it was cold. Egg- 

 to-fry survival was correlated with rainfall, air temperature, and number of eggs deposited. Mean 

 age of return of a brood year was positively correlated with its abundance. The return to escapement 

 ratio for even-numbered brood years was inversely correlated with the abundance (catch plus 

 escapement) of the previous brood year, which suggests that marine survival of chum salmon may 

 be density-dependent. The return to escapement ratio for odd-numbered brood years was positively 

 correlated with early downstream migration of chum salmon fry relative to pink salmon, 0. gor- 

 buscha, fry and with increased chum salmon spawning escapements relative to those of pink salmon. 



Stocks of chum salmon, Oncorhynchus keta, in 

 British Columbia and Alaska have fluctuated 

 considerably in abundance (Hoar 1951; Wickett 

 1958; Hunter 1959; Helle 1979). These fluctua- 

 tions have been attributable to variability in 

 freshwater and marine survival, and have been 

 related to climatic factors such as rainfall (Wick- 

 ett 1958) and to population density or predation 

 on fry (Hunter 1959). Chum salmon in British 

 Columbia return to spawn in their natal streams 

 mainly as 3- and 4-yr-olds, and to a lesser extent 

 as 5-yr-olds. The mean age of returning adults 

 tends to be greater for stocks from northern 

 British Columbia than from southern British 

 Columbia (Pritchard 1943; Ricker 1980). Chum 

 salmon tend to spawn later in the fall than other 

 species of Oncorhynchus, and the fry migrate 

 downstream in the spring, within a few days 

 after emerging from spawning beds. 



The chum salmon stocks of the Fraser River 

 have supported commercial fisheries in John- 

 stone Strait, the Strait of Georgia, and the Fraser 

 River for many years (Palmer 1972) (Fig. 1). 

 Annual catches of chum salmon were extensive 



■Department of Fisheries and Oceans, Fisheries Research 

 Branch, Pacific Biological Station, Nanaimo, B.C., Canada 

 V9R 5K6. 



department of Fisheries and Oceans, Field Services 

 Branch, 1090 West Pender Street, Vancouver, B.C., Canada 

 V6E 2P1. 



Manuscript accepted April 1982. 



FISHERY BULLETIN: VOL. 80. NO. 4, 1982. 



in Johnstone Strait during 1951-54, ranging from 

 0.7 to 2.0 million fish, and in the Fraser River, 

 ranging from 274,000 to 479,000 fish. However, 

 the annual contribution of Fraser River chum 

 salmon to the Johnstone Strait catch is unknown 

 before 1964. Catches of chum salmon declined 

 substantially during 1965-69, ranging from 

 23,000 to 649,000 fish in Johnstone Strait (an 

 estimated to 228,000 Fraser River chums), and 

 10,000 to 196,000 fish in the Fraser River. Catches 

 have continued to vary widely in the 1970s. 

 Fraser River chum salmon have thus shown 

 marked fluctuations in abundance, and these 

 fluctuations have not been satisfactorily account- 

 ed for. It is not currently possible to identify 

 stocks of Fraser River chum salmon, so for pur- 

 poses of the analysis, Fraser chum salmon were 

 treated as a unit stock. This paper describes the 

 population biology of Fraser River chum salmon 

 and results of studies on the causes of variability 

 in the number of returning adults. 



MATERIALS AND METHODS 



Estimates of abundance of returning adult 

 and downstream migrating fry were derived by 

 different sampling methods. Fry were enumer- 

 ated during 1965-81 on the lower Fraser River 

 near Mission City (Fig. 1) using techniques pre- 

 viously described by Todd (1966) and Bailey 



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