Variation in adult life history and morphology among Lake Washington sockeye salmon (Oncorhynchus nerka) populations in relation to habitat features and ancestral affinities

A.P. Hendry and T.P. Quinn
Can. J. Fish. Aquat. Sci./J. Can. Sci. Halieut. Aquat. 54(1): 75-84 (1997)

Abstract: Body size, age composition, and male body depth were compared among five Lake Washington sockeye salmon (Oncorhynchus nerka) populations. Two of the populations (Bear and Cottage creeks) were indigenous to the watershed and three (Cedar River, Issaquah Creek, and Pleasure Point) were non-native (from Baker Lake, Washington). To isolate the relative contributions of habitat type and ancestral relatedness to phenotypic variation, we compared populations with (i) the same origin and similar habitats, (ii) different origins and different habitats, (iii) the same origin and different habitats, and (iv) different origins and similar habitats. Spawning salmon in the Cedar River were older and larger than those in the native populations, a result consistent with their origin (contemporary Baker Lake fish were also large and old) and with habitat variation (the Cedar River is much larger than Bear and Cottage creeks). Body size and age composition did not differ among the three non-native populations, but the body depth of males spawning on the lake beach (Pleasure Point) was greater than that of males in the Cedar River, suggesting adaptive divergence. Adaptive convergence may also have occurred because the population in Issaquah Creek (intermediate-sized creek) did not differ appreciably from those in Bear and Cottage creeks.