NOAA Fisheries’ 2023 5-year review finds that the southernmost endangered steelhead (Oncorhynchus mykiss) populations in California warrant continued protection as an endangered species under the U.S. Endangered Species Act.
The southern California coast includes rivers and streams from the Santa Maria River (Santa Barbara County) to the Tijuana River at the U.S. Mexico border (San Diego County). Steelhead runs in all of these watersheds have experienced sharp declines. Now they are the rarest and most critically endangered steelhead populations on the West Coast.
During the most recent extended drought, steelhead that migrate to and from the ocean have nearly disappeared. The resident form that do not migrate to the ocean has continued to persist, principally in the four U.S. national forests in southern California.
“The risk of permanently losing the anadromous form of the species over the long term is high,” said Lisa Van Atta, Assistant Regional Administrator in NOAA Fisheries' West Coast Region. “It is also increasing due to barriers on migration corridors between the Pacific Ocean and upstream spawning habitat.”
Comprehensive conservation action is required to prevent extinction and promote recovery of these southern California populations.
"Drought and wildfires have taken their toll on the remnant steelhead populations in southern California,” said Mark Capelli, recovery coordinator for the species. “With the assistance of local, state, and federal partners, a significant number of fish passage barriers have been removed or are in the planning stages, which will open up important drought refugia habitat for these highly endangered populations."
The 5-year review highlights the declining population trends in response to drought conditions and the effects of wildfires in all five of the Biogeographic Population Groups within southern California. Smaller watersheds along the Conception Coast and the Santa Monica Mountains have been particularly hard hit with extensive wildfires. Many streams had no flow for multiple years. Larger watersheds, particularly in the southernmost Mojave Rim and Santa Catalina Gulf Coast, have also experienced decreased flows connecting upstream steelhead spawning and rearing habitats with the ocean.
The prolonged drought and extensive wildfires, coupled with climate change, and ongoing land and water development, increases the urgency of recommended recovery actions. These actions were identified in NOAA Fisheries’ 2012 Southern California Steelhead Recovery Plan. They include:
- Reconnecting upper and lower watersheds by removing or modifying dams and other fish passage barriers
- Restoring flows in mainstems and tributaries
- Restoring riparian and estuary habitat
- Controlling non-native invasive plants and aquatic predators
- Reducing excessive groundwater extractions
- Protecting local remnant steelhead populations
Implementing recovery actions will help rebuild depleted and locally extinct populations and increase the species’ resilience.
In addition, plans for the removal of two major dams in core recovery watersheds are nearing completion: Matilija Dam on Matilija Creek (a tributary of the Ventura River), and Rindge Dam on Malibu Creek.
The review also summarizes new research that indicates that the sea-run form of the species can be reconstituted from some populations of rainbow trout. These trout persist in drought refugia, such as those in the four U.S. national forests of southern California. Prior to current human-made barriers, periodic local extinction and regeneration of steelhead runs likely occurred naturally in southern California. Currently nearly all the drought refugia that would help steelhead populations rebound are above impassable barriers. This underscores the importance of restoring fish passage between lower and upper reaches of core recovery watersheds.
The southern California steelhead 5-year review is one of 28 reviews of West Coast salmon and steelhead species by NOAA Fisheries’ West Coast Region. The Endangered Species Act calls for a review of listed species at least every five years to determine if their listing status remains accurate or should be changed. The reviews also provide a report card on recovery, as outlined by each species’ recovery plan. The reviews identify the most critical threats to the species, and recommend key conservation actions that can increase the species’ likelihood of recovery.
The last five years have been challenging for West Coast salmon and steelhead. Climate change and related impacts continue to degrade fish habitats, reducing summer flows and warming water temperatures. In southern California, an extended drought persisted from 2012 through 2022. It reduced flows to historic lows and dried up many rivers that typically provide summer habitat for rearing steelhead. Extended closure of river mouths by sandbars has resulted in fewer opportunities for steelhead to enter coastal watersheds and reach upstream steelhead spawning and rearing habitats. The most recent rains in southern California have temporarily alleviated some of these impacts. However, projected prolonged droughts pose an ongoing threat to steelhead populations throughout southern California.
A series of marine heatwaves has also reduced steelhead ocean survival and growth in the North Pacific Ocean. They increased algal and diatom blooms that affect the productivity of steelhead prey or shift the species to less suitable prey. For the California Current region, sea surface temperatures reached record high levels from 2014–2016; 2015 was the single warmest year in the historical record. Increasing ocean acidification and projected changes in coastal upwelling along the California Current are expected to make it more difficult for steelhead to grow and mature. This will reduce the number, size, and condition of steelhead returning to their freshwater habitat to reproduce.
The southern California populations of steelhead are among the most endangered steelhead on the West Coast. According to the viability assessment completed by the NOAA Fisheries’ Southwest Fisheries Science Center, many of these populations face a high risk of extinction, particularly those at the southernmost extent of the species’ range in the Mojave Rim and Santa Catalina Gulf Coast. Current trends for this species remain of concern, with no observed runs in virtually any of the southern California watersheds during the past 5 years.
Climate change poses a systemic, long-term threat that will require ambitious conservation action to prevent local extinctions and ultimately promote the recovery of the species.
Recent research has improved our understanding of the genetic architecture underlying mixed coastal populations of steelhead and rainbow trout. This includes a better understanding of how the relationship between the migratory and non-migratory form of the species contributes to the survival of both forms.
Research has also documented dispersal of steelhead from nearby and distant watersheds to non-natal watersheds. Dispersal could be an important mechanism for naturally re-colonizing habitat where steelhead have been lost in southern California as a result of physical modification. Causes of this habitat modification include construction of artificial barriers such as dams or road crossings and natural environmental perturbations including, wildfire, debris flows, droughts, or catastrophic floods.
NOAA Fisheries—in cooperation with the California Department of Fish and Wildlife—has completed a comprehensive steelhead monitoring plan. It integrates steelhead viability monitoring, recovery plans, and fisheries management in the Southern Coastal Area of California. The monitoring strategy provides a more efficient and rigorous method of updating future status reviews, and tracking the effectiveness of recovery actions.
This recent research and monitoring guidance gives managers of southern California steelhead a greater understanding of the way in which steelhead and rainbow trout mutually sustain each other. It provides new tools to direct the recovery of the endangered and rare southern California steelhead.
Future progress in the recovery of this endangered species will require the continued collaboration of a wide variety of stakeholders to implement recovery actions.
NOAA Fisheries has released the 2023 5-year review for steelhead populations in southern California protected by the U.S. Endangered Species Act.
The review provides an updated:
- Summary of the listing history of the species
- Description of the criteria used to assess the status of the species
- Report on steelhead research since the last status review
- Information on the status of individual steelhead populations
- Assessment of on-going and emerging threats to steelhead habitats
- Summary of recovery actions undertaken for individual steelhead populations
- Assessment of current state and federal regulatory and funding programs
- Report on broad-scale climate and related ocean changes,
- Comprehensive set of recommendations for future steelhead recovery actions