Science Spotlight

Steelhead are among California's most remarkable fish. Born in freshwater streams, these ocean-going rainbow trout can migrate hundreds of miles to the Pacific Ocean before returning to the very streams where they hatched to spawn. Understanding where steelhead live, how they use habitat, and how many adults return each year is critical to conserving these iconic fish.

“The best way to understand and support this unique species is to monitor steelhead throughout the year using a variety of scientific techniques tailored to each season,” according to Deena Hansen, the California Department of Fish and Wildlife (CDFW) senior environmental scientist supervisor who oversees steelhead monitoring across the South Coast Region for the Department in southern California.

Summer through Mid-Fall: Surveying Young Fish

As weather conditions dry out and stream flows recede during the summer and fall, biologists conduct electrofishing and snorkel surveys to assess juvenile steelhead and resident rainbow trout populations. Occasionally, adult steelhead may spend their summers in freshwater, though it is less common.

Electrofishing uses a battery-powered backpack to send a controlled electric shock into the water. The electric current temporarily stuns fish, allowing scientists to net them and transfer them to buckets. Biologists then identify species, measure individuals, evaluate their health, and document where they occur before quickly returning them to the water. In areas where water clarity and habitat conditions allow, snorkel surveys provide another effective way to observe fish in their natural environment with minimal disturbance.

These surveys help scientists understand where steelhead are thriving, how they use available habitat, and how environmental conditions influence survival.

Late Fall through Early Summer: Tracking the Return Home

When rain arrives and river levels begin to rise in the fall and winter months, adult steelhead begin their migration back to freshwater to spawn.

During this critical period, CDFW biologists conduct redd surveys, searching streams for the gravel nests, known as redds, that female steelhead construct to lay their eggs. Steelhead and rainbow trout are the same species, but while steelhead migrate from freshwater to the ocean, rainbow trout spend their entire lives in freshwater. Counting redds helps estimate spawning activity and identify important spawning habitat. Steelhead redds stand out from resident rainbow trout redds because they are typically larger, reflecting the larger size of the adult steelhead.

In some watersheds, sonar cameras complement traditional field surveys by allowing scientists to monitor fish migrations without handling the fish. “Sonar cameras are like a fish finder, except they look across a river from bank to bank instead of down to the bottom," according to Hansen. The equipment is especially valuable in high-flowing or turbid, sediment-rich watersheds where other sampling methods may not be effective, and because it operates around the clock, it allows biologists to continuously monitor fish movement. These systems provide valuable information on the timing and number of returning adults while minimizing disturbance during spawning season.

Young steelhead develop into smolts and after spending 1 to 3 years in freshwater, they begin their migration to the ocean. This typically occurs from late winter through early summer when higher flows trigger outmigration. CDFW biologists use a variety of monitoring techniques to better understand their survival and movement. In addition to tracking juvenile steelhead as they migrate to the ocean, CDFW biologists use a variety of monitoring techniques to monitor or capture fish in different watersheds, including:

• Acoustic telemetry: Small transmitters are attached to fish, allowing scientists to track their movements and survival as they travel through rivers and estuaries.
• Passive Integrated Transponder (PIT) tag arrays: Tiny electronic tags implanted in fish are detected by stationary antennas, helping biologists monitor migration timing and movement without recapturing the fish.
• Rotary screw traps: Cone-shaped traps placed in rivers safely capture downstream-moving juvenile fish so biologists can estimate abundance, migration timing and overall population trends before releasing them.
• Seine nets: Large nets are pulled through shallow water to temporarily capture fish, allowing scientists to assess species’ composition, abundance and size before releasing them.
• Fyke nets: Funnel-shaped nets that passively capture fish moving with the current, providing information on migration patterns and fish abundance.
• Electrofishing: A carefully controlled electrical current is used to briefly stun fish so they can be identified, measured, tagged or sampled before being released unharmed.

Together, these tools help scientists track steelhead as they make the critical transition from freshwater to the ocean and back, providing valuable information to guide conservation and fisheries management.

Science Across Every Season

No single survey tells the whole story. By monitoring steelhead life stages throughout the year, CDFW scientists build a more complete picture of population health, habitat use, and reproductive success.

“The information collected helps guide our habitat restoration efforts, informs our fisheries management decisions, and supports conservation efforts aimed at maintaining healthy, resilient steelhead populations across California,” said Audrey Dean, one of CDFW Fisheries Branch’s senior environmental scientists that coordinates the statewide California Monitoring Program.

Every season offers another opportunity to learn about these remarkable fish. Together, year-round monitoring helps ensure that future generations can continue to witness one of California's most extraordinary wildlife migrations.

###

Media Contact:
Cort Klopping, CDFW Communications, (916) 201-2958

During the recent 2021-22 drought, CDFW’s Bay Delta Region funded several grant projects focused on conserving streamflow in priority watersheds in Sonoma and Mendocino counties to lessen drought impacts to coho salmon and steelhead trout. One such project, Rain Catchers in Your Neighborhood, led by the North Coast nonprofit Conservation Works, brought the community together to learn about the importance of water conservation and how to catch and store rainwater.

“One of the most rewarding parts of this project was seeing people make the connection between their own water use and conditions in local streams that support coho salmon and steelhead,” said Shay Richardson, the CDFW senior environmental scientist who helped identify and facilitate funding for the project.

Juvenile salmonids seek refuge in pool habitat during the summer months and rely on flow between pools to provide food and maintain suitable temperature and dissolved oxygen conditions. When streamflow becomes disconnected in dry or drought years, large-scale fish die-offs can occur.

Through the Rain Catchers in Your Neighborhood project, rainwater harvesting systems were installed in 2025 and 2026 at community centers within priority coho salmon and steelhead watersheds, including elementary schools, retreat centers and community gardens. Rainwater harvesting systems consist of a roof or other structure to collect rain and a large tank for storage. Participants agreed to use the systems to store rainwater during the rainy season for use during the summer, to offset summer water usage and reduce the need for water diversions in salmon-rearing tributaries in the Russian River and Navarro River watersheds.

Conservation Works installed seven 5,000-gallon systems at community sites and provided 10 rural residential landowners with 5,000-gallon water storage tanks. Conservation Works also partnered with Gold Ridge Resource Conservation District (RCD) to install a 400,000-gallon rainwater harvesting system designed to reduce reliance on summertime groundwater.

Conservation Works invited community members to participate in installation of the 5,000-gallon tanks and also hosted outreach events that focused on water conservation and awareness of drought impacts to salmon and steelhead.

One event provided hands-on educational activities teaching over 400 elementary school students lessons on the salmon life cycle and the importance of using rainwater harvesting to support watershed health. At a community garden site, students from a nearby elementary school visit the garden monthly and use stored rainwater from the tank system to irrigate the garden.

"What we've learned through this project is that people truly care about the impact they make on their ecosystems and simply need regional support to turn that care into action,” said Conservation Works Conservationist Lily Roberts. “Thanks to CDFW and our partner RCD, we were able to bring more rainwater catchment to communities who need it. The tanks provided to rural landowners will leave a lasting mark on the streams, the land and on the families who use them, just as the education we provided to elementary school students will leave its own mark on the next generation."

Following the rainy season, Richardson has visited several of the Rain Catchers in Your Neighborhood project sites to see how the stored water is now being put to use.

“As we anticipate dry conditions this summer, this project highlights how communities can take action in their local watersheds to conserve streamflow and support habitat for coho salmon and steelhead,” Richardson said.

The rain catchment systems are estimated to reduce about 505,000 gallons in annual summertime watershed diversions across Navarro River tributaries (Neefus Gulch, Soda Creek and Meyer Gulch) and Russian River tributaries (Green Valley, Mill, Mark West and Dutch Bill creeks).

###

Media Contact:
Krysten Kellum, CDFW Communications, (916) 825-7120

The Klamath River is back in the news as juvenile salmon are turning up dead, and there are questions about parasites. Here’s what’s happening.

CDFW is working closely with our scientific colleagues at the U.S. Fish and Wildlife Service, Cal Poly Humboldt and Oregon State University to monitor Klamath River salmon and the impacts of the naturally occurring, microscopic C. Shasta parasite (short for Ceratonova shasta). This parasite is common in the Klamath and other Pacific Northwest rivers and its impact ebbs and flows with environmental conditions. Hot weather, warm water and low flows – conditions the Klamath is currently experiencing – can increase its prevalence.

On the evening of May 14, CDFW’s Fall Creek Fish Hatchery released 675,000 certified pathogen-free Chinook salmon smolts into the Fall Creek tributary of the Klamath River about 7 miles upstream of the former Iron Gate Dam location.

The release was also timed when C. Shasta levels in the river had decreased and ahead of forecasted storms, which would improve water quality and accelerate the smolts’ outmigration to the Pacific Ocean. Since then, C. Shasta levels have increased and some of these hatchery fish have been found dead in monitoring traps upstream of the Interstate 5 bridge near the former Iron Gate Dam location. Lab results have confirmed the presence of C. Shasta and another parasite, Parvicapsula minbicornis, in these dead fish. CDFW continues to track the movement of hatchery fish and remains confident that a proportion of Fall Creek Fish Hatchery-origin salmon escaped the impacts of C. Shasta and other parasites.

Additionally, CDFW tributary monitoring of wild juvenile salmon populations indicates the majority of wild fish had already outmigrated ahead of elevated levels of C. Shasta. The C. Shasta parasite does not impact ocean salmon or ocean salmon fishing.

It’s important to understand that some mortality due to pathogens is expected and is a natural part of the salmon life cycle. A pair of Chinook salmon will typically produce around 4,000 offspring but even under ideal conditions, more than 99 percent of those offspring will succumb to pathogens or predation prior to reaching adulthood. While the C. Shasta levels in the Klamath are elevated and somewhat concerning, early spring C.Shasta levels were lower than levels seen in previous drought years prior to Klamath dam removal, and C.Shasta related mortalities in the spring of 2024 and 2025 following dam removal were significantly lower, which are encouraging signs for the future.

CDFW will continue to monitor and track basin-wide conditions through the Klamath Fish Health Assessment Team as adult salmon return to the Klamath River over the summer.

###

Media Contact:
Peter Tira, CDFW Communications, (916) 215-3858