Genetic Variability in Chinook Salmon Stocks from the Columbia River Basin

Abstract

Levels of allozymic variability at 33 protein loci are reported for juvenile chinook salmon Oncorhynchus tshawytscha collected at 28 locations in the Columbia River basin. Fish were classified as spring, summer, or fall run types, depending on time adults reentered the river. Average heterozygosity per sample (H) ranged from 0.023 to 0.097; H over all samples was 0.070 (0.003 SE). On average, fall-run chinook salmon had significantly greater H values than the springor summer-run fish. Spring-run chinook salmon from the Snake River had the lowest values of H (mean, 0.044) in relation to other stocks of spring-run fish, i.e., almost 50% less allozymic variability than spring-run chinook salmon in the lower Columbia River. The probable cause for low levels of heterozygosity in these upriver populations is an increased frequency of natural and humanrelated population bottlenecks. Measures are recommended for hatcheries to maintain effective population sizes and thereby minimize the loss of genetic variability.