Similar survival rates for Pacific salmon in Fraser, Columbia Rivers raises new...( Canadian and U.S. researchers have m...)

Canadian and U.S. researchers have made a surprising discovery that some endangered Pacific salmon stocks are surviving in rivers with hydroelectric dams as well as or better than in rivers without dams.

This is the first study of its kind and is carried out by an international team of scientists that includes researchers from the University of British Columbia. Their findings will appear in the October 28 issue of the open access journal PLoS Biology, published by the Public Library of Science.

The team compared the survival rates of out-migrating, juvenile spring Chinook and steelhead salmon from two river basins: the heavily dammed Snake and Columbia Rivers and the free-flowing Thompson and Fraser Rivers both critical spawning grounds for numerous salmon species.

Using technology that has only recently been available, the team electronically tagged juvenile salmon (smolts) and monitored their journey from freshwater into the ocean via a large-scale acoustic telemetry system called the Pacific Ocean Shelf Tracking (POST) array.

"It came as quite a surprise to us that the Fraser River salmon populations studied have lower survival than the Columbia River study populations," says Erin Rechisky, one of the study authors and a PhD Candidate in the UBC Dept. of Zoology.

Rechisky stresses that there is not yet sufficient evidence to reach any conclusions. "Clearly dams are not good for salmon. What is unclear is whether the Fraser River has a problem that cuts salmon survival to that of a heavily dammed river, or whether factors other than dams play a larger, unsuspected role in salmon survival."

Only in recent years have acoustic tags become small enough for scientists to implant them into juvenile salmon and track them as they migrate downstream. These innovations enabled the team to gather data on salmon smolts in the Fraser River. Before that, it was only possible to measure juvenile survival wher
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