Chinook Salmon’s Last Meal?
A cooler ocean is feeding hungry salmon, but their ultimate survival remains uncertain.
Young Chinook salmon entering the Pacific Ocean this year are finding cooler waters and more plentiful meals than the sea provided their parents. Because of these improved conditions, fisheries scientists forecast a rebound in coming years for the West Coast’s most famous fish. But some researchers and fishermen believe the respite will be temporary, and warn that future generations of Chinook could face even more devastating declines than their ancestors did.
“Things are definitely looking up. I’m pretty optimistic,” says Bill Peterson, an oceanographer at the National Oceanic and Atmospheric Administration, or NOAA, whose ocean monitoring detected the changing environment.
The good news is a welcome change from the latest Chinook headlines. Despite unprecedented fishing restrictions, only 54,000 Chinook are expected to return to the Sacramento River this fall, according to NOAA. Just five years ago, 775,000 came back to the river, and historic numbers—before California’s population boomed with the Gold Rush of 1849—are thought to have been between 1.5 and 2 million.
Three years ago, the Pacific Ocean was in particularly poor shape. Researchers documented large numbers of dead sea birds and skinny whales, along with fewer small fish, shrimp and squid for salmon to eat. “It was horrid,” says Peterson. “Salmon went to sea in 2005, [then] probably died within a couple weeks of getting there, and that’s why there weren’t any fish to come back last year and this year.”
But a recent shift in atmospheric conditions, known as the Pacific Decadal Oscillation, is pushing cold water from the Gulf of Alaska south to the Pacific Coast this year, and with it plenty of plankton—the foundation of the aquatic food chain on which salmon rely. This food source is crucial for oceangoing Chinook that typically spend three years at sea before returning to spawn in freshwater. Returns are therefore expected to fully reflect the ocean’s shift in another two or three years.
Longer-term projections of the Pacific Decadal Oscillation, however, are becoming increasingly difficult. What used to be a relatively predictable cycle of 20- or 30-year warm and cold phases has shortened to 4-year shifts in the past decade. Whether or not these phases are being influenced by climate change remains uncertain. “Maybe in 20 years we’ll look back and say, yeah, this is global warming . . . all the cycles have been upset,” says Peterson. But for now, his attention is on the pending effects of ocean cooling.
The favorable ocean currents “will buy us some time,” says Glen Spain, Northwest regional director of the Pacific Coast Federation of Fishermen’s Associations. “But we have to deal with the problems inland in the meantime.”
The list of freshwater issues is daunting. Hydroelectric dams and water diversions have dried up the Chinook’s traditional migratory paths and spawning grounds. The rivers and streams that remain run shallow and warmer—uncomfortable conditions for salmon. Soil erosion and pollution, as well as natural floods and droughts, further destroy viable habitat. On top of all that, the salmon also face overfishing and an altered ecosystem that includes non-native predators and farmed fish.