Each year since 2002, the Army Corps of Engineers has stationed observers with spotting scopes and along the deck of Bonneville Dam to record the number of salmon and steelhead consumed by sea lions between January and May when ESA-listed runs are present. In 2002, they observed 31 sea lions consume 448 salmon and steelhead in the tailrace area, which extends about one-quarter mile below the dam. The following year, they observed 104 sea lions consume 2,329 salmon and steelhead in the same area. The Corps issues regular reports of its observations in months when California sea lions are present.
Those records are just 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 Bonneville Dam; it does not consider predation that has been observed farther downriver in the lower Columbia River or its tributaries.
14th of March, 2013