What’s that Smelt? Saving San Francisco Bay Delta Native Fishes

Against the current, delta smelt swim frantically in search of juicy plankton, darting towards the surface like thousands of miniature rockets lifting off for orbit. But wait, why are they darting to the surface? Plankton don’t float on the surface of water, they live suspended in it! Well, these delta smelt are among the lucky ones, as they eat gourmet meals at the University of California, Davis Fish Conservation and Culture Laboratory. Captive breeding efforts are underway to preserve this species in the event that they become extinct in the wild—a likely possibility.

Something’s Fishy

Wild delta smelt, however, are not as lucky as these captive fish. Delta smelt are endemic to the San Francisco Bay Delta, meaning they are found nowhere else in the world. In recent decades, these fish have faced numerous challenges in the wild. Consequently, delta smelt have drastically declined in number and are listed as endangered under the California Endangered Species Act.  Some of the obstacles that delta smelt face include habitat loss, pollution, competition from nonnative species in the ecosystem, and water export from the Bay Delta for drinking water and agricultural irrigation.

Unfortunately, delta smelt are not alone in this fight.  Numerous other native fishes in the San Francisco Bay Delta are facing a similar struggle and many pelagic and migratory fish populations are collapsing (e.g., the longfin smelt, Sacramento splittail, Sacramento perch, green sturgeon, Chinook salmon and steelhead trout). As a result, scientists and managers have proposed bringing these fish into captivity by means of conservation hatcheries to prevent their extinction. 

However, there is one problem: many fish hatcheries may actually do more harm than good when they reintroduce captive fish back into the wild. This occurs because captive fish may have accumulated negative genetic changes while in captivity, which may spread into the wild population when they are reintroduced. But hope is not lost!  I’m working on ways to manage fish in conservation hatcheries in an effort to minimize these negative impacts on wild populations and preserve the genetic health of captive fish. 

Hatching a Plan

My project involves studying the life histories of these imperiled fish species to come up with captive breeding recommendations tailored specifically to each species. I am also looking into ways of using genetic information to help manage these fish in captivity and to protect wild populations after captive fish are reintroduced to the wild. My study aims to establish a new culture of hatchery management, which should incorporate considerations of the genetic health of both captive and wild populations. 

Obviously, there is no substitute for habitat preservation or restoration—captive breeding should only be used as a last resort to preserve species that are on the brink of extinction. It is my personal hope that through the conservation work done at the San Diego Zoo Institute for Conservation Research and around the world, there will come a time when there will no longer be a need for captive breeding and “endangered species” will be something that kids only read in their history textbooks. 

In the meantime, we will strive to improve captive breeding to ensure that we maintain genetic health of captive populations and ensure the success of species reintroductions. As for the captive delta smelt, they can rest easy knowing that we will be doing our best to keep them genetically healthy and will keep their gourmet meals coming!

Kathleen Fisch, Ph.D., California Sea Grant Delta Science Program Postdoctoral Fellow at the San Diego Zoo Institute for Conservation Research.
Photos courtesy of B. Mahardja and J. Lindberg