Scientists say Hatchery Steelhead
by Bill Rudolph
Two Northwest scientists say that large releases of hatchery steelhead From the Snake River Basin may hinder recovery of wild chinook salmon. Their analysis was published recently in Conservation Biology (Volume 16, No. 6, December 2002).
"Our results suggest that the release of millions of steelhead from hatcheries in the Snake River Basin was not related to wild steelhead. In contrast, we observed a strong negative association between releases of hatchery steelhead and smolt-to-adult survival of wild chinook salmon," say authors Phil Levin and John Williams, NMFS researchers from Seattle.
The paper theorizes that hatchery steelhead, nearly 10 times bigger than migrating wild spring chinook, may have a competitive advantage. The authors cite a 1986 paper (Dawley et al) that found many chinook with empty stomachs during peak migration periods while steelhead did not.
They also suggest that being barged with steelhead may raise stress levels in chinook that later may increase their susceptibility to predators. Large colonies of Caspian terns and other avian predators feed mostly on hatchery steelhead during the spring. Levin and Williams say the high hatchery steelhead numbers "may help maintain higher populations of predators than would be possible in the absence of hatchery-reared fish. Consequently, chinook may suffer greater rates of predation than they would experience in the absence of hatchery steelhead."
The authors say that any effect hatchery steelhead may have on wild chinook is likely to occur in the river or estuary, rather than in the ocean because the two species have different ocean distributions. Since the negative association is maintained during EL Nino conditions offshore, they say large shifts in ocean productivity "do not dramatically affect the interaction."
The scientists suggest that conventional steelhead hatcheries "may actually exacerbate extinction risks in some cases," but whether such facilities can be reformed "to aide rather than hinder recovery remains unanswered."
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