Columbia River salmon, steelhead and white sturgeon face serious threats from California and Steller sea lions. Since the 1990’s, sea lions have consumed tens of thousands of migrating salmon and steelhead, many from threatened and endangered runs protected under the federal Endangered Species Act (ESA).
The federal Marine Mammal Protection Act (MMPA) of 1972 specifies the actions state fish and wildlife management agencies can take to manage California and Steller sea lions. Recognizing that predation by a growing sea lion population can jeopardize salmon and steelhead stocks at risk of extinction, the US congress amended the MMPA in 1994 to allow States to apply for limited lethal removal authority under a narrow set of circumstances (Section 120 of the MMPA).
In March 2008, fish and wildlife agencies in Washington, Oregon, and Idaho received federal authorization under Section 120 of the MMPA to remove California sea lions that have been observed preying on salmon and steelhead below Bonneville Dam. The federal authorization allows wildlife managers to use lethal measures to remove sea lions that meet specific criteria, although the states’ first priority has been to relocate them to zoos and aquariums.
Removal of problem sea lions has proven to be the most effective means of protecting fish from predation. While exclusion gates keep sea lions out of the fishways, other non-lethal deterrents such as pyrotechnics and rubber buckshot fired at them have only a temporary effect. Wildlife managers from Washington and Oregon and federal and tribal partners have been chasing sea lions away from the area immediately below Bonneville Dam for over a decade.
The California sea lion population along the West Coast is no longer considered at risk and has exceeded its “optimum sustainable population” with the current population at an estimated 300-330,000 individuals, up from less than 75,000 individuals when the MMPA was adopted in 1972. This means removing the relatively few sea lions necessary to reduce the immediate risk to salmon and steelhead at Bonneville Dam will have no impact on the California sea lion population. Of note, all of the sea lions that migrate north of California are males.
Steller sea lions, as a species, are split into separate distinct population segments between the east and west coasts of the Pacific ocean. The Stellers in the Columbia River are from the eastern segment and are currently exceeding 42,000 animals. They were recently delisted from the ESA and down-regulated as not depleted; they could be managed similar to California sea lions if the State wildlife agencies elect to do so. Current salmonid predation by Steller sea lions match the levels of predation California sea lions were having when the States requested Section 120 authority.
Sea lions (especially Steller sea lions) often target sturgeon of spawning age; unlike salmon, sturgeon spawn multiple times in their lifetimes, meaning several generations are lost. In recent years, the number of white sturgeon being consumed by Steller sea lions has declined significantly, but the number of spring chinook eaten by Steller sea lions has increased. The Corps' pinniped monitoring team has documented an increase in the number and duration of stay of Steller sea lions at Bonneville over the last 10 years.