Are Pacific Northwest salmon saving themselves?
It can’t be that simplistic, and yet, Matthew Preusch of the Portland Oregonian reports this morning that a few biologists are seeing signs that some salmon are evolving to survive in Northwest rivers that have been “radically altered” by dams. That includes postponing their migration to the sea until they are larger and better able to survive the hazardous journey to the Pacific. The scientists are studying chinook salmon that this month began spawning in Idaho’s Snake River.
“Traditionally, fall chinook hatch in the spring from eggs embedded in gravel. They enter the ocean as smolts, just a few inches in length, a matter of months later. Then, at sea, they grow up before returning years later to their home rivers, swimming upstream past dams and hundreds of miles inland to spawn in the waters of their birth.
But researchers are finding as many as a quarter of these chinook are staying put in the river for at least a year — either at the mouth of the Clearwater River near Lewiston, Idaho, or further downstream as far as the Columbia River’s estuary — before heading to sea.
The backstory is that as fish numbers plummeted over the past decades, managers reacted by pumping out thousands of hatchery fish and created sheltering cold water pools behind the dams where the fish can shelter and grow over the summers. About a billion dollars have been spent in the effort on the Columbia and Snake rivers.
“They are just growing phenomenally, and I think the reason many of these fish survive is that when they go out in the following spring, they are really hitting the estuary at a good time, and they are so large, there aren’t really many fish that can eat them,” said Kenneth Tiffan, a research fisheries biologist for the U.S. Geological Survey in Cook, Wash., and a co-author of a 2005 study explaining the two life history types.
The researchers say the fish are evolving because enough generations of dam-living fish have occurred and the fish appear to be passing along the trait to their offspring. But other prominent researchers disagree, saying it’s too early to make that determination.
“We have to wait and see over a longer period time,” said Howard Schaller, head of the U.S. Fish and Wildlife Service’s Columbia River Fisheries Program Office. “It’s an interesting piece of information, but there’s a lot of uncertainty.”
— Rita Hibbard