45% of Adult Spring Salmon Not Reaching Bonneville
According to NOAA Fisheries Researchers an astonishing 45 percent of all spring Chinook returning to the Columbia River don’t make it past Bonneville Dam. While it’s difficult to pinpoint any one cause, these same researchers are pointing to sea lions and harbor seals as the primary cause.
Citing information from a study that began in 2010, NOAA biologists tagged more than 2,200 springers in the lower Columbia and monitored their upstream progress the past seven years. NOAA is the federal agency that overseas the Endangered Species Act for Columbia River Basin salmon and steelhead. Survival has varied over the years, but after accounting for harvest, annual survival has ranged from 55 to 90 percent, meaning that as many as 45 percent of the upriver fish tagged in the estuary did not arrive at Bonneville Dam during some years. Genetic testing shows that about 70 percent of the tagged fish are destined for spawning areas and hatcheries in tributaries of the Snake River and the middle and upper Columbia – including threatened species.
It should come as no surprise that the populations of sea lions and harbor seals exploded in the Columbia that year.
“Pinnipeds are probably the primary cause of this mortality, but there are possible other causes,” Dr. Michelle Rub, reported to the Northwest Power and Conservation Council. Those include fish turning into creeks in the lower Columbia to spawn, fish deaths from disease or injury, or even learned behavior – the same seals and sea lions returning year after year to the annual Columbia River salmon feast (most of the sea lions arrive in the spring and leave by summer).
But none of these is as strong a cause as predation by marine mammals, Dr. Rub said.
For example, salmon mortality increases as the population of marine mammals increases each spring. But that hasn’t been the case every year. In 2015, predation declined even with a high population of marine mammals, Rub said.
All things being equal, it further illustrates that sea lions and harbor seals are taking a devastating toll on Columbia River salmon populations.