River dams aren't the main barriers for young Pacific salmon migrating to the ocean, a breakthrough tracking study suggests.
David Welch of Kintama Research in Nanaimo, British Columbia, reports in the journal PLoS Biology that the Columbia River's young salmon and steelhead have as good or a better chance of survival as those in Canada's Fraser River, which is dam-free. The Columbia River has several hydropower dams on its system.
The finding comes as environmental groups campaign to have four Snake River dams removed.
Welch's team used tiny sound-emitting tags on salmon and steelhead released in 2006 from the headwaters of both the Columbia and Fraser rivers, tracking the fish during the smolt stage, when the juvenile fish begin their migration to the Pacific Ocean. Salmon reach maturity in the sea, then later swim back upstream to their hatching site to spawn.
Dramatic declines in the Columbia system have been blamed in part on eight hydropower dams on the Snake 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," says Welch. "We'd have expected to see the survival a lot lower [in the Columbia], but we're actually seeing it's somewhat higher."
The researchers say that while 25 to 65 percent of migrating smolts make it successfully through the Snake-Columbia's entire hydropower system, only a fraction - as little as 0.5 percent some years - return as adults.
The findings are based on technology developed by the Pacific Ocean Shelf Tracking (POST) project, which is headed by the Vancouver Aquarium.
"For the first time we've tracked a critter the size of a hot dog, 1,553 miles (2,500 kilometers) from the Rocky Mountains up to southeast Alaska," Jim Bolger, executive director of POST, told National Geographic News. "One of the other surprises is how quickly they made it - these are the Michael Phelps of small fishes."
