Global Warming

Global Warming Is Pushing Pacific Salmon to the Brink

Pacific salmon that spawn in Western streams and rivers have been struggling for decades to survive water diversions, dams and logging. Now, global warming is pushing four important populations in California, Oregon and Idaho toward extinction, federal scientists warn in a new study.

The new research shows that several of the region's salmon populations are now bumping into temperature limits, with those that spawn far inland after lengthy summer stream migrations and those that spend a lot of time in coastal habitats like river estuaries among the most at risk.

That includes Chinook salmon in California's Central Valley and in the Columbia and Willamette River basins in Oregon; coho salmon in parts of Northern California and Oregon; and sockeye salmon that reach the Snake River Basin in Idaho, all of which are already on the federal endangered species list.

The salmon live much of their lives in the ocean, but they swim far upstream to spawn. In the process, they're a key part of the food chain, including for bears and whales, and they are important to indigenous groups and fisheries along the U.S. West Coast.

The research spells out several ways that global warming endangers the fish. Among them:

- Young salmon die when the water warms above a certain threshold, and droughts can leave salmon stranded or exposed to predators by low water levels.

- Flooding can also flush eggs and young fish from their nests, so the scientists included projections of how global warming will affect extreme atmospheric river rain storms in California as one of the ways to measure the growing threat.

- Warmer stream temperatures have also increased outbreaks of fish disease that can affect salmon, including pathogenic parasites. In May, a toxic algae bloom along the coast of Norway killed 8 million farmed salmon at an estimated cost of about $82 million. In Alaska's Yukon River, a parasite linked with global warming has taken a big toll on the salmon fishery. And in recent weeks, local indigenous observers in Alaska have posted numerous reports of dead salmon in rivers in the western part of the state, as water temperatures reached record highs during Alaska's record-setting heat wave.

- Salmon are also sensitive to changes in ocean currents that carry nutrients, as well as sea level rise, which affects the physical connection between ocean and stream ecosystems, like coastal wetlands in California. Some salmon populations living near the edge of the range of suitable conditions will start to cluster in rivers near the coast, unable to reach their historic spawning grounds unless "access to higher-elevation habitats is restored and habitat quality in rearing areas and migration corridors is improved," the scientists wrote.