Can salmon save themselves?

The Northwest's Columbia River Basin stocks of iconic salmon have been the subject of a heated and expensive court battle for the past decade. Thirteen out of 16 stocks are listed as threatened or endangered thanks to a combination of factors including mining, farming, urban development and most significantly, lots of hydropower dams along the Columbia and Snake rivers.

Some biologists have long argued for the removal of four dams along the Lower Snake River so that the fish can complete their life cycle -- swimming to the ocean and then returning upstream to their place of birth to spawn -- with fewer obstacles and threats. But competing hydropower interests -- namely the federal Bonneville Power Administration which markets the region's hydropower -- have fought tooth and nail for anything but (see HCN’s 2009 feature stories "Columbia Basin (Political) Science" and “Salmon Salvation.”) Federal agencies have poured billions of dollars into alternatives, like trucking salmon around dams, to help the fish survive.

Turns out, some of the fish may actually be helping themselves. Some biologists see signs that the fall chinook salmon may be evolving to weather habitats severely altered by dams, postponing their migration to the sea and growing larger to survive the journey,  The Oregonian reports.

The scientists are studying chinook salmon that this month begin 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.

If these fish -- now called yearling migrants or reservoir types -- survive to be yearlings, they are about eight times as likely to make it back to the river as adults than their counterparts.

"It's just much higher than what you get out of the sub-yearlings," said William Connor, a biologist with the U.S. Fish and Wildlife Service in Idaho. The reason those fish are staying in the river longer, Connor and others think, is because the river is far different than it was 50 years ago.

Some question whether enough time has passed to determine if the adaptations are true evolution, whereby the favorable traits are passed onto offspring genetically. "We have to wait and see over a longer period of time," said Howard Schaller, head of the U.S. Fish and Wildlife Service's Columbia River Fisheries Program Office. "It's hard to say how this is going to translate over the long haul."

Moreover, scientists studied only one stock of fish, says Connor, the U.S. Fish and Wildlife Service biologist. There are hundreds, probably thousands, of stocks of chinook in the Northwest, Canada and Alaska, he says. 

Fish have been known to undergo rapid evolution in response to selective pressures in a changing environment. A study published in The American Naturalist found that Trinidadian guppies had evolved to produce larger and fewer offspring in less than a decade when introduced to water thick with predators.

After the federal and state government cleaned Seattle's Lake Washington, the three-spine stickleback fish underwent "reverse evolution" -- taking on traits that their ancestors had in order to better survive in a cleaner habitat where they are more susceptible to predators. The biggest evolutionary change for those fish occurred during a period of eight years.

Andrew Hendry, a biologist with McGill University in Montreal, said the stickleback study was significant.

"To my mind, it shows how humans can dramatically affect the rate and trajectory of evolution in organisms with which we interact," he said.