Abstract
Investment in fecundity and egg size is compared among two types of chinook salmon Oncorhynchus tshawytscha : stream‐type, which undertake long, arduous oceanic and upstream migrations and often return to their natal rivers (where they do not feed)months before spawning, and ocean‐type, which undertake relatively short oceanic and upstream migrations and remain at sea feeding and accumulating energy until a few days or weeks before spawning. The coefficient of variation in egg size for both life‐history types was significantly less than variation in fecundity, reflecting the expected strong selection on egg size relative to egg number. Total investment in the gonad varied significantly among years in both life‐history types, apparently reflecting variation in oceanic feeding conditions. Stream‐type chinook were smaller in total body size and more than 1 year older than ocean‐type. Stream‐type also invested relatively less of their total body energy in eggs and produced smaller eggs than ocean‐type, reflecting the greater energetic cost of their longer migration and freshwater maintenance. These differences suggest that stream‐type chinook pay a considerable fitness penalty in reproductive output. This may be offset by the fact that stream‐type go to sea at larger size and migrate far offshore, thereby avoiding some of the mortality costs of oceanic migration.