New Science Plan Spurs DWR Efforts for Longfin Smelt

Tucked within the UC Davis campus, a quiet but critically important effort is helping preserve the Longfin Smelt, a vulnerable fish species native to the Sacramento-San Joaquin Delta. Scientists with DWR and UC Davis are collaborating to better understand and conserve this declining species through immediate conservation actions and long-term research.

Longfin Smelt are an indicator of estuarine health. "They can be thought of as the canary in the coal mine," said Brian Schreier, an environmental program manager with DWR, noting their decline reflects broader ecosystem stress. Federally listed as endangered, these fish can live as long as three years. They migrate to the Pacific Ocean during their first year, then return to the San Francisco Bay Estuary and its tributaries to spawn in their second or third year.

Protecting Longfin Smelt means addressing multiple threats. A major concern is entrainment, where fish are drawn into water export facilities. DWR focuses on minimizing these impacts while managing water flows to support spawning and survival. Water quality, contaminants, limited food supply, and predation all threaten the survival of the species.

Captive Rearing Program and Larviculture Techniques

A central component of conservation efforts is captive rearing, which provides a safeguard against extinction and supports research into the species' biology. Through the DWR-supported Longfin Smelt Conservation and Culture Program (LFSCCP), UC Davis researchers are refining methods to raise these fish in captivity. This includes transporting wild adults, acclimating them to controlled environments, and successfully rearing offspring.

A key breakthrough has been successfully rearing fish from the larval stage. According to UC Davis researcher Brianna Yetter, mastering larviculture is essential to producing a stable population in captivity. The process is delicate: larvae are extremely small and sensitive to changes in water quality, flow, and light. Feeding them requires carefully replicating their natural diet with precise timing and composition.

"Mimicking natural diets is an art form," said Yetter.

A Framework for Longfin Smelt Success

These efforts are guided by the Longfin Smelt Science Plan, developed in partnership with the California Department of Fish and Wildlife. The plan outlines research priorities and management strategies to address knowledge gaps during the coming decade. DWR's investment in both the LFSCCP and broader science initiatives supports not only species recovery but also informed operation of the State Water Project.

Despite low population numbers in the wild, researchers have consistently collected adult Longfin Smelt to sustain the captive program. They have successfully spawned fish, reared larvae, transitioned them to dry feed, and raised juveniles to adulthood in both brackish and seawater conditions, all important milestones for the program.

The Importance of Conservation and Collaboration

Still, the urgency remains high. "When populations drop below critical thresholds, extinction risk rises sharply," said Levi Lewis, director of UCD's Otolith Geochemistry and Fish Ecology Laboratory. Raising fish in captivity and potentially releasing them into the wild can help buffer against environmental variability and sudden population crashes.

The broader ecological stakes are also significant. While the loss of a single species may not immediately collapse an ecosystem, cumulative losses can destabilize it. Schreier likens it to a game of Jenga: eventually, removing too many pieces leads to failure, even if the tipping point is hard to predict.

This uncertainty highlights the need for a multifaceted approach that combines habitat restoration, improved water management, and ongoing monitoring and modeling. Collaboration is central to this effort, with DWR, UC Davis, and other state and federal partners working together to strengthen the Longfin Smelt population.

There is cautious optimism among researchers. The program is making steady progress, improving both scientific understanding and practical tools for conservation. Perfecting captive rearing methods also prepares managers for the possibility of future reintroduction efforts if needed.

While challenges remain, this coordinated, science-driven work represents an important step toward stabilizing Longfin Smelt populations and supporting the long-term health of the Delta ecosystem.

Photos of the DWR/UCD collaborative work on Longfin Smelt can be found on DWR's Pixel gallery.