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SOURCE: Inside Climate News

DATE: July 29, 2019

SNIP: 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; 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.

Human infrastructure, including dams and water diversions, were already affecting their streams, reducing the flow and reducing access to the coldest habitats that can serve as a hiding place for salmon during heat waves or drought. Global warming is now intensifying those impacts.

Global warming is already disrupting those cycles for some salmon populations, including sockeye that swim 900 miles to spawn in streams high in the mountains of Idaho.

To spawn successfully, they need exactly the right combination of stream flows and temperatures at exactly the right time of year. But warmer temperatures are rapidly changing the timing of snowmelt and runoff in Western mountains, making it harder for the fish.

Chinook salmon in California’s Central Valley face even more daunting challenges, and some of those populations might be the first to blink out, said University of California, Santa Cruz, researcher Mark Carr, who studies salmon in their coastal habitat.

“California has a long history of destroying the freshwater ecosystems required to maintain strong salmon runs,” Carr said. “If we want salmon around in the future, we need to start working to ensure we have healthy freshwater ecosystems that will better tolerate the changing environmental conditions.”

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. Warmer stream temperatures have also increased outbreaks of fish disease that can affect salmon, including pathogenic parasites. Flooding can also flush eggs and young fish from their nests. 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.