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Extinction Risk for Native Fish if Drought Persists

Peter Moyle, Jeffrey Mount September 10, 2015
FolsomLakeDrought

If the California drought continues, many of California’s native freshwater fishes are at imminent risk of extinction. This is a key finding of our recent report What If California’s Drought Continues?, which projects the potential consequences of ongoing drought on key sectors, including the environment.

Managing scarce water resources to improve the drought resiliency of the state’s rivers, wetlands and forest ecosystems, and the native biodiversity they support, has proven to be the most vexing challenge of this extended drought.

Our research finds that 18 native fishes could go extinct if the drought continues for several more years; this map shows their distribution in the state’s watersheds. We estimated each species’ extinction risk by evaluating the response of these fishes to factors such as reduced flows, increased water temperatures, stress from habitat changes or competition caused by invasive species, and the impacts of hatchery-bred fishes on wild fish populations. (Learn more about our methods in the report’s technical appendix.)

The results are disconcerting. The state’s “anadromous” fishes—those that spawn in fresh water but rear in the ocean—are being hit particularly hard. Coming into this drought, historic water- and land-use practices had diminished their populations. Low flows and high temperatures have made matters worse. Most of the state’s salmon runs are at risk, along with many runs of steelhead trout. Other species—some well-known (delta smelt) and some obscure (unarmored threespine stickleback)—are also in trouble.

The state needs to prepare now for addressing this problem, because if there is another dry year or two, many fishes are likely to go extinct. Recommended actions include acquiring or allocating water (particularly cold water) to improve habitat in strategic locations, relocating some fish, restoring spawning habitat, and improving access of fish to spawning and rearing areas. As a matter of urgency, these species should be brought into conservation hatcheries so that they can be reintroduced to the wild when conditions improve.

Along with the conservation-oriented goal of protecting the state’s native biodiversity, there are also very practical reasons for taking urgent action to protect these fishes. Half of the 18 species at risk are not currently protected under the Endangered Species Act (ESA). Listing species for ESA protection brings legal obligations to stop population declines; experience shows this can be disruptive to water supply operations and incur considerable long-term costs. An ounce of prevention, in this case, would be worth many pounds of cure.

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