"Our work suggests that steelhead released from hatcheries may increase the extinction risk of wild populations of Snake River chinook," say Phillip Levin and John Williams of the National Marine Fisheries Service in Seattle, Washington, in the December issue of Conservation Biology.
West Coast hatcheries have produced salmon for more than a century and today release more than a billion each year. Most of the salmon in the Columbia River Basin are hatchery-reared, including more than 70% of both steelhead and spring-run chinook adults.
Despite these enormous hatchery releases, wild steelhead have dropped 75% in the last 30 years and wild spring-run chinook have dropped more than 95% in the last 40 years. While some people think hatcheries are contributing to these declines, little is known about how hatchery-reared fish affect wild populations.
Levin and Williams used existing population estimates to see if there is a link between hatchery steelhead and the survival of wild salmon (steelhead and chinook) in the Snake River, which is the Columbia's largest tributary. The researchers measured survival by comparing how many juveniles migrated toward the sea (smolts) with how many adults returned over the course of 20 years (1977-1997). The number of hatchery steelhead released ranged from about 4 to 10 million per year.
The results suggest that hatchery steelhead do not affect wild steelhead, but that they may threaten wild chinook. "We observed a strong negative association between releases of hatchery steelhead and smolt-to-adult survival of wild chinook salmon," say Levin and Williams. Specifically, when hatchery r
Contact: Phillip Levin
Society for Conservation Biology