Salmon Survival Rates in Dammed and Undammed Rivers Raise New Questions

In a first-of-its-kind study that may raise more questions than it answers, researchers have found that some Pacific salmon stocks are surviving in rivers with hydroelectric dams as well as they do in rivers without dams.

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.

"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 Department of Zoology.

"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."

The team electronically tagged juvenile salmon and monitored their journey from freshwater into the ocean via a large-scale acoustic telemetry system called the Pacific Ocean Shelf Tracking (POST) array. Current conservation efforts focus on helping smolts pass through the hydropower system. However, the scientific team aims to clarify with future studies whether dam passage in itself has long-term detrimental effects on salmon's ocean survival.

The researchers note that threats beyond the rivers are taking a heavy toll on salmon. These include habitat destruction, competition with hatchery fish, harvesting and large-scale changes in ocean climate. The study’s lead author is David Welch with Kintama Research in Nanaimo.