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, that
amount of water was enough to keep pools interconnected, allowing young salmon
to survive through the hot, dry summer months.
The study can be found at https://www.onlinelibrary.wiley.com/doi/abs/10.1002/tafs.10057
"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 had hit
crisis levels by the early 2000's, and they 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 set up 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 found that low streamflow in summer is one of the biggest
bottlenecks to coho recovery. She says, "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
Water is a limited resource in the Mediterranean
climate of central California. Population growth and development, combined with
the impacts of climate change in the drought-prone region have made
flow-impaired streams even less reliable.
While previous modeling studies have
established water flow thresholds to support salmon in larger, snowmelt-fed
streams such as those in California's central valley, the small coastal streams
where Russian River coho prefer to spawn are a different beast.
These intermittent streams may swell over
their banks during wet winter months but dwindle to a trickle or even dry up in
sections during the hot, dry summer. While it was clear that young salmon
needed more water to survive the summer months, the question was, how much?
"We didn't have a sense of how much water
was needed," says Obedzinski. "The existing models are based on flows
in much larger streams. When you try to apply them to our tiny coastal streams,
they fall apart."
The 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,
and 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 is a project manager for the Gold
Ridge Resource Conservation District, who has already begun applying the new
research to their work restoring flow in salmon streams. He says, "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."
The researchers stress that flows allowing for
minimum persistence are not high enough to support full recovery. Obedzinski
says, "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. In terms of meeting recovery targets, more
water means more habitat for fish, and more chance of bringing back a healthy
NOAA's California Sea Grant College Program
funds marine research, education and outreach throughout California.
For more than a decade, California Sea Grant's
Russian River Salmon and Steelhead Monitoring Program has been conducting
broad-scale salmon and steelhead monitoring, along with specialized studies, in
order to provide science-based information to all stakeholders involved in the
recovery of these critical native species. The program supports the Russian
River Coho Salmon Captive Broodstock Program, the statewide Coastal Monitoring
Program, the Russian River Coho Water Resources Partnership, and other salmonid
recovery efforts throughout the watershed.