Spatial and Temporal Factors Affecting Survival in Coho and Fall Chinook Salmon in the Pacific Northwest
Abundance and survival of Pacific salmon have been declining. Of several hypotheses advanced to explain the declines, the major ones attribute declines to genetic deterioration, disease accumulation, variations in oceanic conditions, and density-dependent mortality. To test some of these hypotheses, we estimated the survival rate of hatchery releases of coho and fall chinook. The data consisted of mark and recapture rates of codedwire-tagged fish from the northeastern Pacific Ocean. The mean survival by hatchery and location was analyzed by means of graphs, generalized linear models, and cluster analysis. The results indicate that salmonid populations continue to decline in most of the geographical range. The declines are particularly marked from the late 1970s to the early 1980s and from the late 1980s to the most recent years available. Age of the hatchery is of little or no importance, so disease accumulation and genetic changes are not the causes of the observed survival declines. Some hatcheries continue to have good survival rates for long periods. The overall results indicate that changes in ocean conditions could be at least partially responsible for the survival declines of coho and chinook in the Pacific Northwest.
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Document Type: Research Article
Publication date: 1998-03-01
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