for National Geographic News
The first ever tracking of young Pacific salmon ocean migrations suggests the main barriers to their survival aren't river dams—but lethal obstacles at sea.
The controversial finding, which makes use of the latest in fish-tagging technology, investigated the seaward migration of Chinook salmon and steelhead—a type of trout—in North America's two largest West Coast rivers.
Juvenile fish equipped with tiny sound-emitting tags were released in 2006 in the headwaters of Columbia River, which has numerous hydropower dams on its system, and Canada's dam-free Fraser River.
A team tracked the fish during the "smolt" stage of their life cycle, when the juvenile fish begin to migrate—as they headed for the Pacific Ocean and distant feeding waters off Alaska.
Salmon reach maturity in the sea, then later swim back upstream to their hatching site to spawn.
Dramatic declines in Pacific salmon and steelhead in the Columbia system have been blamed in part on eight hydropower dams on the Snake.
Conservation groups are campaigning to have four of these dams removed.
But David Welch of Kintama Research, Nanaimo, British Columbia, reports in the journal PLoS Biology that the Columbia's young salmon and steelhead have as good or a better chance of survival as those in the Fraser River.
"This doesn't mean that dams are good for salmon, but it's a very different result than what the science community would have expected," Welch said.
"We'd have expected to see the survival a lot lower [in the Columbia], but we're actually seeing it's somewhat higher," he said.
While the new study focused only on the river stage of the smolt migration, mortality levels at sea are also being investigated by the team.
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