Small Amounts of Water Make a Big Difference for Endangered Salmon

A University of California San Diego study says even small amounts of running water could mean the difference between life and death for juvenile coho salmon in coastal California streams.

The study, published in early June in the journal Transactions of the American Fisheries Society, shows that during dry periods less than a gallon of water per second was enough to keep pools interconnected, allowing young salmon to survive through the hot, dry summer months.

“The good news is that if we can get just a little bit of water back in these streams, we can make a really big difference,” said Marika Obedzinski, a California Sea Grant extension specialist. Obedzinski is the lead in a monitoring program for endangered coho salmon and steelhead in small streams of Sonoma County that flow into the Russian River.

Russian River coho salmon were listed as threatened in 1996, but despite efforts to improve habitat, the species hit crisis levels by the early 2000’s and became endangered in 2005 when scientists noted fewer than 10 fish returning to the Russian River annually to spawn. Local, state and federal agencies teamed up to start a conservation hatchery program to breed and release the fish. The Sea Grant monitoring program was set up to track the success of the hatchery releases and to better understand factors that were preventing recovery of the species. Researchers found that low streamflow in summer is one of the biggest blockers to coho recovery.

“After the hatchery fish are released, we see them migrating out to the ocean and coming back as adults to spawn,” Obedzinski said. “We even see their offspring in creeks in the early summer, but by late summer the creeks dry out, the young salmon die, and the next generation is not surviving.”

Water is a limited resource in central California, an area impacted by population growth, development and climate change. While intermittent streams may overflow their banks in wet winter months, they may dwindle to a trickle or dry up in sections during the summer.

The new study offers a clearer link between salmon survival and water flow rates in Russian River tributaries, which could be useful for resource agencies and organizations working on salmon recovery, and land owners who want to help restore endangered salmon populations.