Ancestry of Southern California Steelhead and Rainbow Trout

SWFSC Fisheries Ecology Division researchers from the Molecular Ecology and Landscape Ecology teams have published a paper demonstrating that steelhead / rainbow trout (Oncorhynchus mykiss) above major dams in five large river systems in the endangered Southern California DPS (Distinct Population Segment) and threatened South Central California DPS region are descended from coastal steelhead lineage fish trapped above the dams at construction.

Millions of hatchery rainbow trout have been released above these dams and in nearby streams, but the study also failed to detect substantial reproductive contribution from these hatchery trout. The discovery of substantial reservoirs of genetic variation for these two ESA-listed DPSs, and minimal hatchery trout introgression, is good news for recovery efforts, although careful attention needs to be paid to the consequences of many generations of selection against anadromy in these residualized steelhead populations.

Clemento, A.J., E.C. Anderson, D. Boughton, D. Girman, and J.C. Garza.
In press. Population genetic structure and ancestry of Oncorhynchus mykiss populations above and below dams in south-central California. Conservation Genetics.

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(November 4, 2008)