Testing the impact of dam passage on homing success in salmon

Snake River salmonids are federally protected, but face a succession of dams to navigate from the ocean to the spawning grounds. The final dam in the sequence is the Lower Granite Dam. Ascending salmonids (sockeye salmon, steelhead, and Chinook salmon) all enter the fish ladders on the side of the dam, but some pass straight through and exit above the dam, while others are shunted off to one side and either released after a longer pathway, or held in tanks and sampled before being released to continue up the fish ladders. These three different passage routes allow for a statistical analysis to detect whether their homing success is affected by the sampling method, revealing that free passage is better than shunting, but that trapping did not affect detection rates in spawning areas compared to those that were shunted but not trapped. However, since a substantial fraction of salmonids are held in tanks for 15-20 hours before sampling, and these had lower homing success than those held for short periods, it would be wise to alter the trapping protocols to reduce the holding time. The new work by Christina Morrisett and Prof John Skalski of SAFS, and Russell Kiefer at the Idaho Department of Fish and Game, appears in the North American Journal of Fisheries Management.

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