Three quarters of California’s trout and salmon are at risk of extinction over the next century because of climate change, drought and other threats, a report by UC Davis and CalTrout warned Wednesday.

The report reviewed all 31 species of the state’s native trout, salmon and steelhead — together known as salmonid fish — and concluded that 23 of those are likely to disappear within 100 years. Of those, 14 species could go extinct within 50 years, the report stated.

Among the most imperiled is the Southern Steelhead, an ocean-going trout native to Southern California waterways, including several creeks and rivers in San Diego and Orange Counties. Others include commercially important salmon runs in Central and Northern California.

The potential loss could damage the state’s salmon fisheries and $7 billion inland sportfishing sector, and also herald broader environmental crises, said Curtis Knight, executive director of CalTrout.


“If you love fish, you love to go fishing, that’s a concern,” he said, but added, “These are more than just resident fish. Their health indicates the health of our waters, which are important for all Californians.”

The report, entitled “State of the Salmonids II; Fish in Hot Water,” built on a similar study of the fish conducted in 2008. It found that after the five-year drought and recent warming trend, their condition has deteriorated. The authors hope the report can serve as a starting point for conservation efforts that could include dam removal, protecting key rivers, improving fish habitat, and restoring springs and meadows that serve as water sources.

“The impacts of climate change have become much clearer than they have been in the past,” said author Peter Moyle, professor emeritus in the Department of Wildlife, Fish and Conservation Biology and Associate Director of the Center for Watershed Sciences at UC Davis. “Almost universally, California’s salmonids are worse off at this point in time.”

Salmon and trout are important in human history, appearing in Cro-Magnon cave art of 10,000 years ago, and in the diets of people throughout the world, the report noted. California, with 31 species, and habitat spanning coastal streams and alpine lakes, has more types of these fish of any of the lower 48 states, the authors said.


“Salmon, trout, and their relatives are the iconic fishes of the Northern Hemisphere,” the report stated, adding that the fish thrive in “the region’s cold, productive oceans, rushing streams and rivers, and deep cold lakes. They are adapted for life in dynamic landscapes created by glaciers, volcanoes, earthquakes, and climatic extremes.”

Many of the species move between ocean and freshwater systems, and all have weathered extreme conditions for millennia, but climate change and other environmental challenges are testing their resilience, the report stated. One of the biggest threats is the lack of cold, clean water caused by rising temperatures, extended drought and decreased stream flow.

Loss of habitat caused by dams and cities, changes in the food web, and shifting ocean conditions are also taking a toll. Changes in ocean current, and ocean acidification related to climate change are reducing the food supply in the open ocean, where many of these species live and grow. And sea level rise is flooding coastal lagoons and estuaries that are important for young salmon and steelhead. Some wild fish are also breeding with hatchery stock, they said, creating hybrid fish that lack the diverse characteristics of the separate species.

To rate their status, the authors reviewed each species according to seven criteria, including the area they occupy, abundance of adult fish, their dependence on human intervention, tolerance for changes in water temperature and chemistry, genetic risk, climate change, and other human-caused risk factors.


They interviewed fishery experts and reviewed scientific literature to score the species’ risk of extinction. Only one species — coastal rainbow trout — appeared to be at low risk. The rest were ranked at moderate, high or critical risk, with Southern Steelhead falling in the latter category.

The fish, listed as federally endangered, used to swim freely in creeks and rivers of coastal Southern California. Photos from the last century show anglers packed on stream banks during steelhead runs of up to 55,000 fish per year, according to estimates by the National Marine Fisheries Service. An ocean-going strain of rainbow trout, steelhead are born in freshwater, travel to the sea, and return to their birthplace to spawn. Despite their adaptability, the fish nearly vanished in the latter part of the last century, and number fewer than 500 today.

Conservation groups have long sought to restore the fish to Southern California streams, but the effort, like the steelhead’s journey, has been an uphill climb.

In 2011, the California Coastal Conservancy cancelled plans to bolster steelhead in San Mateo Creek, which cuts through Camp Pendleton to the Cleveland National Forest, after their efforts to control predatory frogs and non-native fish failed. Farther north, plans to remove the Matilija Dam from part of the Ventura River to restore steelhead spawning grounds have been in the works for two decades.


However, the South Coast Steelhead Coalition is still trying to improve steelhead habitat on San Mateo Creek, and the Santa Margarita and San Luis Rey Rivers, according to CalTrout’s website. And the Escondido Creek Conservancy aims to rehabilitate and eventually reintroduce the iconic fish to the urban creek.

Steelhead tolerate warmer water than most other trout or salmon, and can switch entirely to freshwater when their route to the ocean dries up.Although the fish are some of the most critically endangered in Southern California, they are also some of the most resilient, and offer clues that could help other fish populations weather hot water, Moyle said.

“Southern steelhead is truly an amazing fish in that it is persisting in part of the state down to San Diego, where it’s highly urbanized,” Moyle said. “To me they’re a magnificent fish. People get really thrilled to see these big fish coming up the stream. Right now we’re making choices whether we want to have those fish with us in the future. And I’m hoping we do. It just takes some hard choices as far as water allocation.”

deborah.brennan@sduniontribune.com Twitter@deborahsbrennan