Ecology of Kokanee Salmon and Rainbow Trout in Crater Lake, Oregon

Abstract

ABSTRACT Originally barren of fish, Crater Lake was stocked with approximately 1.8 million salmonids from 1888 to 1941. Rainbow trout (Oncorhynchus mykiss) and kokanee salmon (O. nerka) now inhabit the lake. This study was conducted from 1986 to 1991 to document and compare kokanee salmon and rainbow trout ecology in the lake to better evaluate the ecological implications of the presence of these non-native fish. Kokanee salmon exhibited cyclic patterns in population age structure, condition, abundance, and biomass from 1986 to 1991. One dominant year class of relatively low abundance and high condition was present from 1986 to 1987. Multiple year classes with increasing abundance and decreasing condition were present from 1989 through 1991. Rainbow trout maintained a diverse population structure throughout the study with a trend toward a relative increase of older age classes and larger fish. Vertical and horizontal migrations of kokanee salmon occurred within and between the nearshore and offshore zones...