Wednesday, February 29, 2012

New Study Indicates "Segregated" Hatcheries are Ineffective at Minimizing Impacts on Wild Fish


A new study published yesterday in the Journal Evolutionary Applications, is giving credence to those who have long insisted that segregated hatcheries do not effectively minimize gene flow between hatchery and wild steelhead. The study used genotype data to track hatchery and wild populations over three generations from the beginning of the steelhead hatchery program in Forks Creek, a tributary of the Willapa. The authors found was that despite generations of selection for early run timing and a weir intended to reduce spawning interactions between hatchery and wild fish, over time the degree of hybridization between early run Chambers creek stock and wild winter steelhead increased to the point that as many as 80% of unmarked (non-hatchery origin) returning adults had some degree of hatchery ancestry.

Throughout the state WDFW releases several million early timed Chambers creek stock winter steelhead every year. The long held belief among managers being that these fish are subject to high levels of harvest, spawn earlier than their wild counterparts and are therefore unlikely to interbreed with the wild population. However in Forks Creek, despite high harvest rates in the Willapa, and a weir designed to stop upstream passage of hatchery fish, high water events in most years allowed hatchery fish to escape into the river above the weir and spawn among their wild counterparts. This is a major concern for the sustainability of the wild run within Fork Creek since Chambers Creek fish are known to have very low fitness when spawning in the wild.

Preliminary results from work on tributaries of the Skagit have shown similarly high rates of hatchery introgression despite the fact that the steelhead hatchery there is managed as a segregated program. These results also highlight the risks posed by ongoing releases of Chambers Creek stock steelhead in the Elwha throughout the dam removal and recovery period, and the importance of a recent agreement between the Lower Elwha Klallam tribe the Wild Fish Conservancy, Wild Steelhead Coalition, Conservation Angler and the FFF Steelhead Committee in which the tribe agreed not to release Chambers creek steelhead into the Elwha this year. With an ongoing 5 year fishing moratorium on the Elwha, all of the returning Chambers creek stock fish would have spawned in the wild posing a severe threat to the fragile population of ESA listed winter steelhead remaining below the dam.

Read the article

Seamons et al. 2012 - Can interbreeding of wild and artificially propagated animals be prevented by using broodstock selected for a divergent life history.

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