New study from California Sea Grant researchers shows that during dry periods, a small amount of water can be enough to keep young salmon alive during the hot, dry summer months.

Adapted from original article by Katherine Leitzell, California Sea Grant

Even small amounts of running water—less than a gallon per second—could mean the difference between life or death for juvenile coho salmon in coastal California streams, according to a new study published in the journal Transactions of the American Fisheries Society.

The study, led by California Sea Grant Extension Specialist Mariska Obedzinski, shows that during dry periods, relatively small amounts of water were enough to keep stream pools connected, allowing young salmon to survive through the hot 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,” says Obedzinski, who leads a monitoring program for endangered coho salmon and steelhead in the 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 became endangered in 2005 when scientists noted fewer than 10 fish returning to the Russian River each year to spawn. In response, local, state, and federal agencies teamed up to start a conservation hatchery program to breed and release the fish. California Sea Grant’s monitoring program was put in place to track the success of the hatchery releases as well as better understand the factors that were preventing recovery of the species.

Through their monitoring, Obedzinski and her research team identified low streamflow during summer as one of the biggest bottlenecks to salmon recovery.

“After the hatchery fish are released, we see them migrating out to the ocean and coming back as adults to spawn. 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,” says Obedzinski.

This new study provides 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, as well as for land owners who want to help restore endangered salmon populations. The findings may also lend support for efforts that might seem small-scale in comparison to larger streamflow improvement projects in other watersheds.

John Green, a project manager for the Gold Ridge Resource Conservation District, has already begun applying the new research to the District’s work restoring flow in salmon streams.

“The big value in this research is that it has given us an idea of how much water is needed to improve fish survival. From that, we start to understand the kinds of projects we need to build and what their impacts will be,” notes Green.

The study’s authors stress that flows allowing for minimum persistence are not high enough to support full recovery.

“Keeping a pool connected is the first step in preventing local extinction by keeping at least some of the fish alive, but we want fish to be able to grow and thrive as well,” says Obedzinski, “In terms of meeting recovery targets, more water means more habitat for fish, and more chance of bringing back a healthy population.”

This work is part of California Sea Grant’s mission to provide integrated research, extension, outreach, and education to help Californians balance diverse interests that intersect with the coastal and marine environments and adapt to changing conditions and needs.