CRONE and BOND: LIFE HISTORY OF COHO SALMON 



were 43—1964 brood coho salmon that had spent 2 

 yr in fresh water; and in 1969, 29% of the adults 

 were 54—1964 brood coho salmon that had spent 3 

 yr in fresh water. Another large brood year in- 

 dicated by the ages of returning adults is the 1967 

 brood. No similar patterns of a strong brood year 

 are evident in the 4 yr of data from Sashin Creek 

 coho salmon (Table 7). 



Direct comparison of the many studies on age 

 composition of coho salmon must be done with 

 caution because of year-to-year variations and 

 different sampling techniques, but a general clinal 

 change in freshwater and total age with latitude is 

 suggested— southerly populations are predomi- 

 nantly age 3.2 and northerly populations predomi- 

 nantly age 43. In British Columbia, Washington, 

 Oregon, and California, coho salmon (exclusive of 

 jacks) are almost all age 3_> (Pritchard 1940; Marr 

 1943; Smoker 1953; Shapovalov and Taft 1954; 

 International North Pacific Fisheries Commission 

 1962). Gilbert (1922) reported that about 60% of the 

 coho salmon of the Yukon River were age 43; the 

 remainder were age 3^. Coho salmon populations 

 in most streams studied in the Cook Inlet-Kenai 

 Peninsula area of Alaska are composed of 60% to 

 95% age 43 fish (Andrews 1962; Logan 1963; Engel 

 1966; Kubik 1967; Redick 1968). In the Karluk 

 River system on Kodiak Island, Alaska, age 43 fish 

 also are dominant but age 54 fish, rather than age 

 3^, are the second most abundant (Drucker 1972). 

 Semko (1954) listed age composition of coho salm- 

 on from the Bolshaya River, Kamchatka, for 8 

 yr; in two of the years (1946 and 1947) age 43 adults 

 outnumbered age 32. The highest percentage of 

 age 43 fish reported by Semko (1954) was 64.7%. 

 The age composition of coho salmon from the 

 commercial fisheries of the Taku and Stikine rivers 

 in southeastern Alaska in 1955 was 68.0% age 32 

 and 28.2% age 43 (International North Pacific 

 Fisheries Commission 1962). A later report on 

 Stikine River coho salmon caught in 1955 gives age 

 composition as 45.2% age 32 and 51.9% age 43 

 (Godfrey 1965). Of several thousand coho salmon 

 represented by scales collected from the commer- 

 cial fisheries in southeastern Alaska, about half 

 spent one winter in fresh water (age 32) and half 

 spent two winters in fresh water (age 43) (Smoker 

 1956). Nearly equal numbers of ages 82 and 43 also 

 were reported for coho salmon at Hood Bay Creek 

 in southeastern Alaska (Armstrong 1970). 



Fecundity 



We determined the fecundity of female coho 



salmon from Sashin Creek in 1966, 1970, and 1971 

 and, for comparison, from nearby Nakvassin 

 Creek in 1966-72 (Table 8). Most of the females 

 from Sashin Creek were collected at the weir and 

 the rest were collected with sport fishing gear in 

 the estuary (a total of 3 to 22 each year). All 

 samples from Nakvassin Creek were collected with 

 sport fishing gear in the estuary (6 to 45 females 

 each year). Ovaries from individual females were 

 placed in containers of water and boiled until the 

 eggs hardened and separated from the ovarian 

 tissues. The mean of the annual fecundity samples 

 from Sashin Creek was 3,186 eggs per female (33 

 fish); the fish from Nakvassin Creek were slightly 

 smaller and the mean of the samples was 2,326 

 eggs (116 fish). 



The relation between number of eggs and fork 

 length for Sashin Creek and Nakvassin Creek coho 

 salmon was calculated by the method of least 

 squares regression. The regressions for Sashin 

 Creek and Nakvassin Creek are Y = -441.48 

 -1-51.633X (r = 0.31) and F. = -824.59 -I- 47.686X 

 (r = 0.37), respectively. Y is the estimated number 

 of eggs and X is the fork length in centimeters of 

 females. Log transformations of number of eggs 

 and fork length did not increase the values of r 

 significantly. 



Average fecundities of coho salmon reported for 

 other streams range between 1,983 and 5,343 

 (Table 9). Although these values were derived in 

 many different ways and therefore are not strictly 

 comparable, a general trend of increasing fecun- 

 dity from south to north and east to west does 

 appear. 



Table 8.-Mean and range of fecundity and length of female 

 coho salmon from Sashin Creek in 1966, 1970, and 1971 (3 to 22 

 fish) and Nakvassin Creek in 1966-72 (6 to 45 fish). 



In 1965 and 1967, dying and dead spent female 

 coho salmon were examined for retained eggs 



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