Delta Smelt Experiment

February 8, 2024

Question: What’s the latest on CDFW’s experiment with the Delta smelt population?
Answer: CDFW continues to work alongside several partner agencies to learn more about the decline of Delta smelt and what might be possible to aid in the survival of the endangered species.

The Delta Smelt Experimental Release Study involves releasing 90,000 laboratory-raised fish into the Delta this season to determine which methods prove the most effective at production, tagging, transport and release of the fish into the wild. Learning which plan works best could someday help to supplement the population with a goal of aiding in the recovery of the species.

While being raised in captivity, each fish is marked by hand with an adipose fin clip or a fluorescent tag. A particular color indicates to scientists the date, location and experimental method of the release.

Recently 32 metal 20-gallon containers were filled with 200 Delta smelt and emptied directly into the Sacramento River into a specially designed submerged cage. The cage provided a safe environment while the fish adjusted to the river temperature and their new surroundings before they were fully released a few hours later into the river. Through Delta smelt monitoring surveys that are conducted routinely each year, CDFW can learn about their health and survivability.

“Last year was the first time we were able to uniquely mark fish from different experimental release events and get decent numbers of adult fish recaptured in our monitoring surveys,” said CDFW Environmental Program Manager Dr. James Hobbs. “We’re releasing adult fish just before the spawning season, and we’re hoping these fish will meet up and produce the next generations.”

Unfortunately, the same factors responsible for the near disappearance of the fish are still present including a less than reliable flow of freshwater, low food productivity, loss of wetland habitats, predation by non-native species and other reasons. But scientists say the experiment is showing some positive results with survival and recovery of released adults.

February 8, 2024

Question: What’s the latest on CDFW’s experiment with the Delta smelt population?
Answer: CDFW continues to work alongside several partner agencies to learn more about the decline of Delta smelt and what might be possible to aid in the survival of the endangered species.

The Delta Smelt Experimental Release Study involves releasing 90,000 laboratory-raised fish into the Delta this season to determine which methods prove the most effective at production, tagging, transport and release of the fish into the wild. Learning which plan works best could someday help to supplement the population with a goal of aiding in the recovery of the species.

While being raised in captivity, each fish is marked by hand with an adipose fin clip or a fluorescent tag. A particular color indicates to scientists the date, location and experimental method of the release.

Recently 32 metal 20-gallon containers were filled with 200 Delta smelt and emptied directly into the Sacramento River into a specially designed submerged cage. The cage provided a safe environment while the fish adjusted to the river temperature and their new surroundings before they were fully released a few hours later into the river. Through Delta smelt monitoring surveys that are conducted routinely each year, CDFW can learn about their health and survivability.

“Last year was the first time we were able to uniquely mark fish from different experimental release events and get decent numbers of adult fish recaptured in our monitoring surveys,” said CDFW Environmental Program Manager Dr. James Hobbs. “We’re releasing adult fish just before the spawning season, and we’re hoping these fish will meet up and produce the next generations.”

Unfortunately, the same factors responsible for the near disappearance of the fish are still present including a less than reliable flow of freshwater, low food productivity, loss of wetland habitats, predation by non-native species and other reasons. But scientists say the experiment is showing some positive results with survival and recovery of released adults.

Jim's still on the case!