Management Options for Salmon on the Snake River
Dams in the Columbia River basin have contributed to severe declines in wild salmon runs there. Of the twenty-four salmon runs in the West that are listed under the Endangered Species Act (ESA), twelve are in the Columbia River and four must pass through dams on the lower Snake River. Dams have eliminated salmons' access to large parts of eastern Washington, eastern Oregon and Idaho and southern British Columbia, and on many reaches that remain open to them spawning populations average 10 percent or less of 1950 levels.
The Army Corps of Engineers is considering breaching the Snake River dams to recover salmon. A recent paper in Science used a numerical model to determine which combinations of survival rates during the salmon's life resulted in a growing population1. Remarkably, the study found that even if every juvenile fish that hatched in the upper Snake River survived the passage to the ocean, and if every returning adult fish made it up the river to spawn, the population would continue to decline towards extinction. The model indicates that modest reductions in mortality in other parts of the salmon's journey would reverse population declines. Removal of the dams on the Snake River would undoubtedly improve conditions for the salmon, but that by itself would not be enough to insure their survival. We spoke with Michelle McClure, one of the authors of this important contribution to our understanding.