Nearly all rivers along the entire North Pacific Coast—from southeast Alaska to southern Oregon—are experiencing similar or worse trends in Chinook salmon returns when compared to the lower Columbia and lower Snake rivers. This applies to coastal inland rivers in British Columbia and the Puget Sound as well. These poor returns are being observed in rivers with dams and without dams, and even includes rivers with nearly pristine habitat.
(Chinook, sockeye, and steelhead are the three species that are experiencing these lower returns. Other salmon species, like chum and pink, have remained more stable.)
Scientists theorize the problem is occurring in the ocean. Some believe growing numbers of seals and sea lions, which feed on the fish, are behind the declines. Others say the warming and acidifying of the ocean is killing off the prey that the salmon depend on. There is strong evidence that ocean conditions, including ocean temperatures, are an important predictor of adult salmon returns.
Outdoor Life, “Why are Alaska’s chinook salmon runs crashing? It’s a big mystery that a salty group of researchers aim to crack”
CBC, “More than a dozen B.C. chinook salmon populations in decline, scientists say”
Anchorage Daily News, “Southeast Alaska’s king salmon are disappearing, and fishermen are grappling with the consequences”
NOAA Fisheries Fact Sheet – Southern Resident Killer & West Coast Chinook Salmon