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NW Fishletter #276, June 18, 2010

[8] New Predation Study Begins on Bass Note

Funding has been approved for a new study of predation on salmon smolts by smallmouth bass at several federal dams on the Columbia River.

The report will also look into the role of shad in the food chain of reservoir-dwelling fishes. Shad, probably the most famous non-native fish in the Northwest, return to the Columbia by the millions, yet scientists have never understood just how they fit into the river's ecosystem.

Smallmouth bass are also an introduced species, but classed as a game fish by WDFW. It is thought they consume large numbers of smolts at several mainstem dams.

The study, led by researchers from the U.S. Geological Survey and ODFW, will begin a quantitative look at the issue, prodded by language in the 2008 hydro BiOp that calls for managers to find ways to reduce populations of non-indigenous fish.

The Northwest Power and Conservation Council approved initial funding at its June meeting--$350,000 for an FY 2010 planning budget--after the proposal got a provisional green light from the independent science panel that reviews F&W projects. The science panel was concerned whether the investigators would be able to capture enough smallmouth bass in dam forebays and tailraces to make adequate comparisons.

The study will look at suspected "hot spots" for smallmouth bass in the forebays at McNary, John Day and The Dalles dams, and try to compare them to tailrace areas thought not to be hot spots for the bass, based on pikeminnow catch data.

The proposal will also try to figure out the role of juvenile shad in the diets of non-native predators.

A 2008 regional workshop shared the skimpy knowledge among biologists.

Researchers said that smaller smallmouth bass were the most predaceous and grew large enough to eat salmon by two years of age. It's thought that older bass concentrate on prey other than salmon.

The bass also tend to focus on the smaller naturally-produced fall chinook instead of the larger hatchery-produced yearlings.

Others at the 2008 meeting noted that "a lot of people really like bass fishing, so there could be sub-stantial opposition to removal -B. R.

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NW Fishletter 255

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