Experimental release paves the way for multiyear supplementation program
By Gary Pitzer, US Bureau of Reclamation
Federal and state agencies recently took the unprecedented action of releasing captive-raised Delta smelt into the cold, murky water of the Sacramento-San Joaquin Delta just south of Rio Vista. This first experimental release is part of a multiyear effort aimed at preserving an endangered fish found only in the Delta that’s on the verge of extinction. The multi-agency collaboration released about 12,800 fish in three days and will do additional releases in the next month to reach a total annual release of approximately 40,000 fish.
“This experimental release is a big step forward on understanding how a supplementation program could work” said David Mooney, area manager of the Bureau of Reclamation’s Bay-Delta Office. “This is an important tool to support Delta Smelt as we continue our efforts to better understand all the stressors impacting fish populations.”
The Delta smelt’s struggle is emblematic of the relative health of the Delta ecosystem.
Most of the 2-inch Delta smelt complete their lifecycle in about a year and are hatched, mature and reproduce within the slightly salty to freshwaters of the Delta. They are an indicator species for the Delta, meaning their survival or disappearance reflects the overall health of the estuary.
Once a prominent species in the region, the Delta smelt population rapidly plummeted in the early 2000s. They were once one of the most abundant species in the Bay-Delta, and now are only rarely seen in surveys and trawls. For decades, the changes wrought on the Delta by drought, climate change, water quality, land development, water diversions, and other factors have adversely affected living conditions for Delta smelt.
That dilemma prompted a response by Reclamation and its partner agencies. In its 2020 Long Term Operating Plan for the Central Valley Project and State Water Project, Reclamation outlined the need to take actions to protect Delta smelt, leading to this year’s collaborative experimental release. The released fish are mature and can be expected to spawn in the next couple of months.
Delta smelt are produced at the UC Davis Fish Conservation and Culture Laboratory, which Reclamation funds. The laboratory maintains a population of genetically managed Delta smelt and supports research on captive-bred fish. Plans are in place to expand the laboratory facilities to increase rearing capacity to provide as many as 125,000 smelt each year.
