A recent Endangered Species Act 5-year review shows water use, habitat loss, and climate change continue to compromise recovery.

By NOAA Fisheries

Northern California steelhead require continued protection as a threatened species under the U.S. Endangered Species Act, according to a recent 5-year review by NOAA Fisheries. State and federal agencies, tribes, and private landowners have completed numerous habitat restoration projects since the last review in 2016. However, the population faces continued threats from drought, high water temperatures, and water use, all exacerbated by the changing climate. The 5-year review also found that water conservation should be integrated into habitat restoration projects to achieve maximum benefits.

“Because climate change is one of the most significant threats to Northern California steelhead, protective efforts in the future should focus on projects that aim to conserve water during the summer and fall low flow periods,” said Seth Naman, a fish biologist with NOAA Fisheries and the lead author of the 2024 5-Year Review: Summary & Evaluation of Northern California Steelhead.

The range of the Northern California steelhead (Oncorhynchus mykiss) extends from Redwood Creek in Humboldt County south to the Gualala River in Sonoma County. They were first listed as threatened under the Endangered Species Act in 2000. For rivers and streams with enough data to analyze trends over time, populations have either no trend or slightly decreased numbers of returning adults since the last 5-year review. Several streams did not have enough information available to analyze population trends over time, which remains a concern.

Summer-run steelhead face particularly acute threats from high water temperatures and low water flow. Adults spend 4 to 6 months in deep pools in rivers and streams during the summer. For virtually all populations of Northern California steelhead with enough data, current population estimates are less than 15 percent of ESA recovery goals.

The 2014 California Water Action Plan charged the State Water Resources Control Board and California Department of Fish and Wildlife (CDFW) with enhancing water flows. Enhanced flows were required in at least five stream systems that support critical habitat for steelhead and Pacific salmon. This includes the Eel River, which provides habitat for the greatest number of steelhead in the region.

Cannabis Regulation Benefits Steelhead

Another regulatory measure that has improved protection of Northern California steelhead was the legalization and regulation of cannabis. California voters passed Proposition 64, the Adult Use of Marijuana Act, in 2016. Subsequent legislative action gave CDFW the authority to ensure that cannabis cultivation does not adversely impact steelhead and salmon habitat. The regulation of recreational cannabis has also had a downstream effect on the market by lowering prices, making illegal grow operations uneconomic. This has prompted unpermitted growers to close up shop and stop illegally diverting water, Naman said.

Overfishing was not found to be a factor that threatens Northern California steelhead. There is no commercial fishery for the species in the region; bycatch in commercial harvests have not been found to be a significant source of mortality. Recreational fishing for steelhead is popular, but has limited impacts. CDFW manages the recreational fishery and enforces the catch and release of steelhead throughout their geographic range.It has set a bag limit of two hatchery steelhead on the Mad River.

Research indicates marine mammal populations have increasingly preyed on salmon and steelhead populations in the eastern Pacific Ocean in recent decades. These animals are recovering under the Marine Mammal Protection Act. Further study is required to understand whether or not marine mammal predation is contributing to slower recovery of imperiled salmon and steelhead populations, including Northern California steelhead.

Long-Term Threats of Climate Change

The long-term impacts of climate change pose the most significant threat to the viability of Northern California steelhead.  A 2018 study found that California will likely lose nearly all of its tidal wetlands due to sea-level rise. These estuaries and coastal wetlands are important habitats for both juvenile steelhead migrating to the ocean and for adults returning to spawn.

Warming temperatures and drought decrease available habitat for steelhead by reducing streamflows and elevating water temperatures. They also increase the prevalence of wildfires. The 5-year review found that since the last review there has been “increased frequency and severity of large, unprecedented wildfires” in Northern California. These blazes increase sediment from ash, topsoil runoff, and landslides in steelhead and salmon streams. They also lead to even warmer stream temperatures, as the shade provided by tree canopies is lost.

Rising ocean temperatures, ocean acidification, toxic algal blooms, and other oceanographic changes alter the ecosystems and food webs in the North Pacific. This leads to shifts in the abundance of both predators and prey. A growing consequence of this is thiamine deficiency caused by an increased abundance of anchovies and an absence of other prey.

Recommendations for Long-Term Success

Northern California steelhead, like all salmonids, need cold, clean water to thrive. The primary recommendation from the 5-year review is to “support and fund projects intended to increase stream flows during the summer and fall months.”

The 2014 California Sustainable Groundwater Management Act brought statewide legislation regarding how the state manages its groundwater resources for the first time. However, the regulations appear inadequate to protect Northern California steelhead. Additional streamflow protections are required to ensure Northern California steelhead have sufficient flow levels during the summer and fall months.

A positive development for Northern California steelhead is the coming removal of both Cape Horn and Scott dams on the Eel River. This will likely provide substantial benefits to the Eel River basin and Northern California steelhead by opening approximately 300 miles of potential steelhead and salmon habitat. This habitat had been closed off by the dams since their construction more than 100 years ago. This large-scale restoration project should be prioritized by state and federal agencies, tribes, and private landowners for implementation in the years to come. In the marine environment, researchers should further study the effects of both marine mammal predation and thiamine deficiency on Northern California steelhead, Naman said.

“Northern California steelhead are resilient and can recover, as long as protective efforts including water conservation and forward-looking regulatory actions and habitat protection are enacted, allowing them to flourish,” Naman said.