Age and Morphology of Chum Salmon in Southern British Columbia

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Abstract
Differences in sex ratios by age, age compositions, gill‐raker frequencies, and morphometric characters were investigated for stocks of chum salmon Oncorhynchus keta spawning at different times and in different river sizes in southern British Columbia. For all stocks pooled, males were more abundant than females at 3 and 5 years of age, but less abundant at 4 years. Early‐spawning stocks from tributaries of the Fraser River and from rivers on Vancouver Island had older age compositions (means, 4.03 and 3.92 years, respectively) than did later‐spawning stocks (means, 3.64 and 3.73 years, respectively). Early‐returning stocks from all rivers also had fewer gill rakers (21.9) than did late‐returning stocks (22.3). Males had larger heads, thicker caudal peduncles, and larger dorsal fins than did females, but females had larger anal fins than males. Chum salmon from large rivers (regardless of when they spawned) had larger body parts (head, fins, caudal peduncle) than did chum salmon from small rivers or creeks. Chum salmon are adapted morphometrically to water availability and flow in their natal streams and these adaptations provide part of the rationale for salmonid homing. Received October 31, 1983 Accepted July 1, 1984