Dams Appear to Have No Impact on Salmon

The heavily dammed Columbia and its largest tributary the Snake River in the northwestern United States serve as a breeding ground to millions of salmon, including endangered chinook and steelhead species, which have been dwindling steadily for years.

Whether or not the eight dams along the rivers contribute to the decline has been a source of bitter controversy for decades. Conservation groups, the commercial and sport fishing industries and local Native American tribes have long blamed the fishes' plight on the dams. Government agencies have responded by sinking some $600 million into the watershed for research, and building structures like fish ladders that reduce the dams' impact on fish.

Now a new study published yesterday in the journal PloS Biology suggests the measures are working.

David Welch of Kintama Research in Canada, a company that develops equipment for tracking marine life, and colleagues tagged 1,000 young chinook and steelhead salmon in the Columbia-Snake rivers and the undammed Fraser River in British Columbia. They tracked the fish as they navigated out to sea through the rivers, and then compared survival rates in the two rivers.

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In the Columbia they found the fish survived just as well, if not better than fish swimming down the Fraser River even though they have to swim 600 kilometers (373 miles) further. To account for the difference the researchers measured fish survival per 100 kilometers (62 miles) of swimming.

By that metric 80 percent of young fish survived per 100 kilometers, versus 60 (37 miles) in the Fraser.

"I was bowled over," Welch said. "Everybody including me thought we'd see much lower survival in the Columbia."

However, Welch said the results don't mean dams are good for fish. They may have a long-term impact on survival that the researchers didn't see.

"Their survival rate in the ocean is about one-half of one percent," he said. "So there's still a problem, but it's mainly because of whatever is happening to them in the ocean."

This year, salmon populations along the west coast of the United States plummeted, prompting the federal government to close fisheries in California and much of Oregon. Congress approved $170 million in emergency funding to blunt the damage caused to commercial and sport fishing industries in the region.

Ray Hilborn of the Unviersity of Washington ascribes much of the decline in salmon population to natural climate cycles like El Nino and La Nina, which can affect ocean temperatures throughout Pacific northwest.

"Changes in water temperature can affect the distribution of predators," like the salmon shark, a close relative of the great white shark seals, and sea lions, Hilborn said.

"Right now most of what we're seeing is probably not due to anthropogenic climate change," he said. "In a 100 years that could be a very different story."

Related Links:

Kintama Research

Upper Colorado River Endangered Fish Recovery Program