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Extinction Ahead: Bracing for the end of Delta Smelt

The iconic fish, native to California, could see its last days in the wild as a result of the ongoing drought.

Written by Peter Moyle Published on Read time Approx. 4 minutes

I saw my first Delta smelt in 1972, during my first fall as an assistant professor at UC Davis. I was on a California Department of Fish and Wildlife trawl survey to learn about the fishes of the Sacramento-San Joaquin Delta. The survey was targeting young striped bass, but the trawl net towed behind the boat captured large numbers of the native Delta smelt.

I remember a single haul with a couple hundred of these iridescent, finger-length fish being dumped into a container on deck. I decided to study smelt biology because these fishes were so abundant and yet so poorly understood. I would have no trouble collecting enough of them for my research.

Lee Miller, the biologist in charge of the surveys, started preserving the smelt catches for me. Each year for three years a pickup loaded with quart bottles of Delta smelt, as well as longfin smelt, would arrive at my laboratory. For a diet study alone, my technician and I dissected 1,055 Delta smelt.

Today, few Delta smelt remain in the wild. Researchers get their samples from special labs where the smelt are bred in captivity.

The state’s 2014 fall midwater trawl survey showed the lowest number of Delta smelt in 47 years of record keeping. In early March, the state conducted its annual spring trawl survey, designed to capture Delta smelt as they aggregate to spawn. They caught only six smelt — four females and two males.

The dismal catch prompted me to advise the state’s Delta Stewardship Council that Delta smelt appear to be approaching the point of no return, with extinction in the wild possible in the next year or two.

I say “in the wild” because there are two captive populations of smelt. The U.S. Fish and Wildlife Service manages a backup population at its fish hatchery below Shasta Dam, and UC Davis produces smelt for experimental and conservation purposes at a lab in the Delta, just south of Stockton. Both facilities raise hundreds of smelt through their entire life cycle. Each fish is tagged and its genetics recorded for precise mating, to maximize genetic diversity. Each year a few wild smelt are brought in to mix their genes with those of the captive brood stock.

We don’t know what the minimum population size has to be for successful reproduction of Delta smelt in the wild. But it must be hard for males and females even to find one another today, and even harder to find partners that are in the right stage of maturity for spawning. Most of these fish have a one-year life cycle, apparently dying after spawning. A few live two years. This means a bunch of them have to spawn successfully every year to maintain a viable population.

We don’t know with absolute certainty that wild Delta smelt will disappear within the next couple of years. But the likelihood is high enough that we should be prepared for it. We need to start answering a lot of questions, like these:

  • How do we know when the Delta smelt is truly extinct in the wild? Who makes the decision? (It is worth noting the last thicktail chub was caught in the Delta’s Steamboat Slough in 1957, but the fish was not recognized as extinct for at least 30 years).
  • Should the last of the Delta smelt be captured so their genes can be added to the captive population, as was done for the California condor?
  • Can captive populations be used to restore smelt in the wild? (Not easy to answer: It won’t work as long as the conditions that caused smelt to decline remain, including competition and predation by alien species, altered food supply, water pollution and water diversions upstream and within the Delta. The extended drought presumably has worsened these conditions and pushed the smelt over the edge of the extinction cliff, or at least close to it.)
  • How does management of the Delta change if smelt are extinct in the wild? Today it is hard to do anything water-related in the Delta without considering impacts on smelt, particularly operation of state pumping facilities and wastewater treatment plants. What happens when the species is gone?

Presumably, protecting Delta smelt has benefited other native fish because it is the species most sensitive to changes in the Delta’s waterways. Other listed fish species that affect and are affected by Delta management include winter- and spring-run Chinook salmon, longfin smelt, green sturgeon and Central Valley steelhead.

We need to prevent more fish from reaching the cliff-hanger status of Delta smelt. We need to extend proactive management from species already listed to those headed in that direction, including hitch, blackfish, splittail, tule perch and white sturgeon. This requires learning more about their requirements and managing parts of the ecosystem specifically for their benefit, including tidal marshes.

I hope we still have enough smelt and enough time to keep the species from altogether disappearing from the Delta. But, as my geologist colleague Jeffrey Mount is fond of saying, “Hope is not a strategy.” We need to be planning for Delta smelt extinction and, perhaps, its resurrection.

Peter Moyle, a professor of fish biology, is associate director of the Center for Watershed Sciences at UC Davis. He can be reached at [email protected].

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