USE OF COLUMBIA RIVER RESERVOIRS FOR REARING BY JUVENILE FALL CHINOOK SALMON AND SOME MANAGEMENT IMPLICATIONS

Abstract

ABSTRACT Historical early life history patterns of fall Chinook salmon have been altered by impoundment of the Columbia River. While growth rates remain high, riverine survival has been reduced by impoundment, passage mortality at dams, predation, disease, thermal stress, and possibly, late ocean entry. Late ocean entry may reduce fall Chinook salmon survival by delaying passage through a sequence of habitats (spatial windows) at a time, size, or physiological state (temporal windows) when they are best adapted to that habitat. Extended freshwater residence retards higher growth rates normally associated with entry into the estuary and ocean, and reduces the higher survival associated with increased size. Managers of hatchery and wild stocks must take these spatio-temporal windows into account when evaluating management techniques such as flow manipulation or transportation.