Patterns of gametic investment by female stream- and ocean-type chinook salmon

Investment in fecundity and egg size is compared among two types of chinook salmon Oncorhynchus tshawytscha: stream-type, which undertake long, arduou s oceanic and upstream migrations and often return to their natal rivers (w here they do not Feed) months before spawning, and ocean-type, which undert ake relatively short oceanic and upstream migrations and remain at sea feed ing and accumulating energy until a few days or weeks before spawning. The coefficient of variation in egg size for both life-history types was signif icantly less than variation in fecundity, reflecting the expected strong se lection on egg size relative to egg number. Total investment in the gonad v aried significantly among years in both life-history types, apparently refl ecting variation in oceanic feeding conditions. Stream-type chinook were sm aller in total body size and more than year older than ocean-type. Stream-t ype also invested relatively less of their total body energy in eggs and pr oduced smaller eggs than ocean-type, reflecting the greater energetic cost of their longer migration and freshwater maintenance. These differences sug gest that stream-type chinook pay a considerable fitness penalty in reprodu ctive output. This map br offset by the fact that stream-type go to sea at larger size and migrate. far offshore, thereby avoiding some of the mortali ty costs of oceanic migration. (C) 2001 The Fisheries Society of the Britis h Isles.