SOURCE: New York Times

DATE: September 16, 2019

SNIP: Chinook, or king salmon, are huge, powerful fish, the largest member of the salmon family in North America. Spring-summer Chinook make an epic migration thousands of miles through the Columbia River to the waters surrounding Alaska’s Aleutian Islands, and then back to the high elevations of the Rocky Mountains.

Before the 20th century, some 10 million to 16 million adult salmon and steelhead trout are thought to have returned annually to the Columbia River system. The current return of wild fish is 2 percent of that, by some estimates.

While farming, logging and especially the commercial harvest of salmon in the early 20th century all took a toll, the single greatest impact on wild fish comes from eight large dams — four on the Columbia and four on the Snake River, a major tributary.

The four Snake River dams are used primarily to create reservoirs for the barging of Idaho’s wheat to ports. But the dams raise water temperatures and block travel migration routes, increasing fish mortality.

Climate change also has raised both river and ocean water temperatures, which can be deadly to fish. In 2015, for example, unusually warm water killed an estimated 250,000 sockeye salmon.

For decades, experts have tried to ameliorate the loss of the Columbia’s wild fish by installing ladders that allow the fish to swim around the dams, and by placing them in barges and trucks for transport around the dams. The massive efforts have not stemmed the decline, despite the fact that more than $16 billion has been spent on recovery over the last several decades.

Now most scientists come down on the side of removing the dams.

Always a gauntlet, the migration of the salmon now is far more deadly. The eight large dams along the Snake and Columbia rivers created 325 miles of slack water in reservoirs. The average speed of the water flowing downstream has dropped to less than 1.5 miles per hour, and it takes the fish far longer to reach the sea.

When the parrs reach a reservoir on the way, they must swim instead of being pushed by the current, and often become disoriented and are more susceptible to predators. Delayed, they may go through smoltification at the wrong time.

The young salmon eat plankton and insects. But the waters of the Pacific along the West Coast have experienced unusual warming — the so-called blob — which reduces the available food supply.

Before the Snake River dams were built, three to six of every 100 fish that left their natal streams returned home, a ratio called smolt-to-adult return. Today that number is just under one. Biologists say it must reach four to rebuild the fisheries.

It is not just orcas that are suffering because of the decline of salmon. An estimated 137 species rely on the surge of protein brought upriver by millions of fish each year. The salmon also provided phosphorous, nitrogen and other nutrients that nourish the great forests of the Northwest. Three-quarters of the nutrients in some trees in Alaska and British Columbia are derived from salmon.