A warming climate is likely to wipe out spring-run Chinook salmon in at least one California watershed by the century's end, found a new study.
No matter which climate projections the researchers used, warmer waters spelled major trouble for the fish in the coming decades if people do nothing to help the fish. And the findings are likely to apply to a variety of salmon species up and down the West Coast, especially in California where temperatures are closest to the tipping point.
"I saw the results almost a year ago, and I just sat at my desk and cried," said Lisa Thompson, a fisheries biologist at the University of California, Davis. "Fish weren't making it through to the end of the century in almost all cases."
"Things look grim," she added. "But there are things we can do."
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For the last five years, Thompson and colleagues have been studying spring-run Chinook salmon in the Butte Creek watershed, in the Central Valley of California. These types of fish are particularly sensitive to climate change because adults spend their summers in freshwater streams before spawning in the fall. And compared to the Pacific Ocean, where the fish spend the rest of the year, streams are far quicker to warm up in hot conditions.
More than a million spring-run Chinook used to live in the waters of the Central Valley, Thompson said. Today there are fewer than 10,000 of them -- a decline of 99 percent.
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To find out what the future holds for the fish that have managed to hang on, the researchers created a model that factored in all sorts of climate data, including rainfall, temperatures, humidity and wind. They included lots of field data about how the fish respond to various conditions in their summer streams. And to focus just on the effects of freshwater conditions, they assumed that the fish did just fine in the ocean and returned in to their usual streams to spawn.
The study considered six possible scenarios for the future, including "business as usual," in which our greenhouse gas emission rates continue to rise at their current rate. The study also considered the possibility that emissions would level off by the end of the century.
In all scenarios -- even the most hopeful ones -- spring-run Chinook failed to survive to the year 2099, the researchers reported in the Journal of Water Resources Planning and Management.
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"It's not surprising, but it's unfortunate and it's shocking in the magnitude of potential impact," said Howard Brown, a fisheries biologist with NOAA's National Marine Fisheries Service. "It really shows us from a modeling perspective that some of the populations we're managing right now have a real likelihood of going to extinction in a pretty short time frame."
Despite the grim predictions, salmon are not necessarily doomed, Thompson said. For one thing, the fish have proven their resilience before by finding safe hiding spots in extra cool pools or in cold spots near the bottom of streams. She has seen a group of salmon survive hot days by lining up nose to tail in a two-foot wide stream.
The study also offered hope for the fish if managers take measures to help the fish. By leaving water in the creek instead of diverting it to a nearby hydropower plant, for example, Butte Creek's pools could remain deeper and cooler. That, the model showed, would buy the fish at least another decade of survival there. The next question is whether that's an affordable option.
"This has a lot of regional implications and implications across the state and up the West Coast," Brown said. "We need to look at new and adaptive ways of managing fish and habitat areas if we are going to be able to sustain them for a longer period of time."