. . . In California, the dry summer season is a critical period in the freshwater chapters of a salmon’s life. That’s when streams are lowest and water temperatures already approach or even exceed the maximum that the fish can tolerate. “The effects of climate change could be extremely devastating to salmonid populations, especially here [in California] at the southern end of their range,” says Dan Freed, a biologist with the Arcata office of NOAA Fisheries (formerly the National Marine Fisheries Service), the federal agency charged with maintaining the health of salmon runs. “Water temperature and flow are the two big [factors]. There isn’t a lot of room for change to occur before it would be catastrophic.” And higher flows in winter could also be damaging, as they can scour salmon eggs out of the gravel beds where they are laid, and can flush young fish downstream before they are ready.

Of all these effects, “the change in snowpacks is the most troublesome, because salmon expect steady stream flow,” says Zeke Grader, executive director of the Pacific Coast Federation of Fishermen’s Associations. He predicts that silver (coho) salmon and steelhead trout will be most affected by warming, since they spend the longest time in fresh water. Already, he’s seen the balance among salmon populations altered because of conditions in rivers and streams. Fall-run king (chinook) salmon used to be third in importance to fishermen, after their spring-run and winter-run cousins. (The seasons denote the time of year when the adults enter rivers to spawn.) But fall-run fish have come to predominate, he says, because they spend the least time in fresh water, where stream habitat has suffered serious damage from land-use practices. If a warming climate makes streams even less hospitable to fish, more changes along these lines would likely occur.

Recent die-offs of salmon bear out Grader’s warnings. Several thousand spring chinook died in Butte Creek this summer in the wake of a heat wave that made them more vulnerable to disease. The deaths echoed a larger fish kill in the Klamath River in 2002 that claimed an estimated 33,000 chinook, blamed on a combination of high water temperatures and low river flows.

. . . Freed’s description of salmon behavior suggests how to protect the fish from the dangers of climate disruption: to keep salmon populations as robust as possible, and do what we can to reduce the factors that are destabilizing the climate, so that the changes are slower and less severe. In a world where “normal” winters vanish from our experience, that may be the best way to maintain at least one element of normalcy: the annual return of salmon to our streams.

SETH ZUCKERMAN has participated in watershed restoration efforts in the Mattole Valley for 15 years. He is at work on a book about the false divide between people and the rest of nature. Seth Zuckerman has participated in watershed restoration efforts in the Mattole Valley for 15 years. He is at work on a book about the false divide between people and the rest of nature.