CORVALLIS, Ore. A new study by researchers in Oregon and British Columbia has found that survival of juvenile salmon and steelhead during their migration to the sea through two large Northwest rivers the Columbia and the Fraser is remarkably similar despite one major difference.
The Columbia River has a series of dams, while the Fraser has none. However, the researchers point out, there clearly are other differences between the rivers. And though the study using both acoustic and transponder tags found that the average mortality in both rivers was between 70 and 80 percent over a four-year period, the results should be viewed with caution.
Findings of the study were published this week in the journal PLoS Biology.
"Despite the obvious comparison, it would be overly simplistic to say that dams have no impact on smolt survival, because we know they do," cautioned Carl Schreck, a professor of fisheries and wildlife at Oregon State University and the U.S. Geological Survey and an author of the study. "There also may be some additional delayed mortality of Columbia River smolts caused by the stress of passage through the hydrosystem that is not manifested until the fish reach the ocean."
Columbia River juvenile salmon can be stressed by navigating the series of dams from Lower Granite to Bonneville. Other stress-inducers can include water temperature, contaminants, predation attempts, and availability of food, forcing fish to channel their energy into survival instead of growth, Schreck pointed out.
"Stress in fish delays development," he said. "It also suppresses the immune system, which can increase the chance that fish will be susceptible to disease or parasites. Even though these data suggest that the fish survive the freshwater phase of their migration, that kind of weakened condition can be the difference when a young salmon tries to adapt to a salt water environment."
Schreck, a leading expert o
|Contact: Carl Schreck|
Oregon State University