Ask the Department of Fish & Wildlife:
How do fish managers know that California sea lions are preying on runs of Columbia River salmon and steelhead?
Each year since 2002, the Army Corps of Engineers has stationed observers with spotting scopes along the deck of Bonneville Dam to record the number of salmon and steelhead consumed by sea lions between January-May when runs of fish protected by the Endangered Species Act are present. In 2002, they observed 31 sea lions consume 448 salmon and steelhead in the tailrace area, extending about one-quarter mile below the dam. Since then, observers have documented a steady increase both in the number of sea lions and their level of predation. In 2008, observers reported that 103 sea lions consumed more than 4,243 salmon and steelhead in the same area below the dam.
Those observations are one indication of the level of sea-lion predation on Columbia River salmon and steelhead. Another estimate, based on California sea lions’ metabolic needs, suggests that 100 animals feeding in that area consume at least 13,000 salmon each spring. That estimate applies to predation only in the tailrace of the dam; it does not consider predation that has been observed farther downriver in the lower Columbia River or its tributaries.Information for this feature comes from wdfw.wa.gov/help.