A Genetic Monitoring & Evaluation Program for Supplemented Populations of Salmon & Steelhead in the Snake River Basin




Prepared for Bonneville Power Administration


This is the second report of research for an ongoing study to evaluate the genetic effects of using hatchery-reared fish to supplement natural populations of chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. nerka) in the Snake River Basin. The study plan involves yearly monitoring of genetic and meristic characteristics in hatchery, natural (supplemented) and wild (unsupplemented) populations in four different drainages for each species. This report summarizes the first two years of electrophoretic data for chinook salmon and steelhead and the first two years of meristic data for chinook salmon. Results obtained to date include the following: (1) Genetic variation was detected at 35 gene loci in chinook salmon and 50 gene loci in steelhead, both considerable increases over the number of polymorphic loci reported previously for Snake River populations No substantial differences in levels of genetic variability were observed between yeas or between hatchery and natural/wild populations in either species. (2) In both species, statistically significant differences in allele frequency were typically found between years within populations. However, the temporal changes within populations were generally smaller than differences between populations. (3) Differences between chinook and salmon populations classified as spring- and summer-run accounted for little of the overall genetic diversity; in contrast, substantial genetic differences were observed between "B" run steelhead from Dworshak Hatchery and "A" run populations from other study sites. (4) Estimates of the effective number of breeders per year (Nb) derived from genetic data suggest that Nb in natural and wild Snake River spring/summer chinook salmon populations is generally about one-quarter to three-quarters of the estimated number of adult spawners. (5) Analysis of the effects on data quality of sampling juveniles indicates that the small size of some wild fish may lead to a slight increase in the number of missing data points; however, there is no evidence for bias in the data that are collected. (6) Seven bilateral meristic characters in chinook salmon were identified that show promise as indicators of fluctuating asymmetry. Indices of asymmetry varied in a largely random fashion among populations. No correlation was found between the level of asymmetry and the level of genetic variability within individual fish.

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