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Auke Bay Laboratory (ABL)

Marine Salmon Interactions Program

Little Port Walter Studies

Since the mid-1990s, ABL scientists have been conducting studies on rainbow trout (Oncorhynchus mykiss) at the Little Port Walter Research Station (LPW) in Southeast Alaska. These studies investigate genetic and population dynamic relationships between the anadromous form rainbow trout, also known as steelhead, and the resident form. In June 2005, ABL fisheries scientist Frank Thrower presented the results from some of the LPW research to the Puget Sound Steelhead Biological Review Team (BRT) in Seattle. The BRT is tasked with reviewing all available biological information on the current status of O. mykiss populations in the Puget Sound Evolutionarily Significant Unit (ESU) to determine if the populations warrant protection under the Endangered Species Act.

Research results from LPW indicate that populations of rainbow trout that were formerly anadromous but are currently held behind barriers such as dams can still produce offspring capable of smolting and surviving in the ocean, even after the populations have been isolated for decades. Two examples of this in the Puget Sound area exist behind the dam on the Cedar River, a water supply for the City of Seattle, and the Elwa River, which has a hydroelectric dam that borders Olympic National Park.

While these results are valuable in determining whether certain populations should be considered part of an ESU, another important finding was that the smolts produced from formerly anadromous fish held in sequestration for 70 years did not survive in the marine environment as well as those produced from anadromous parents. This significant reduction in marine survival could indicate that production of a healthy, anadromous return from resident fish might take several generations. Researchers at LPW are currently conducting studies to determine if a genetic bottleneck, which occurred 70 years ago, or lack of continuous selection in the marine environment is the main cause of the poor marine survival. Results of this work will help predict the success of specific recovery actions taken to restore endangered populations.

Joshua Clark, a NOAA intern funded by the AFSC, has been helping LPW researchers recover steelhead adults that have coded-wire tags and has also been assisting in the incubation laboratory in evaluating the incubation success of more than 175 individual families of anadromous and resident rainbow trout. Eighty of these families are being placed in individual rearing containers, and Clark will be feeding and caring for them until his internship is completed in late July.

By Frank Thrower

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