[Water_news] 3. DWR'S CALIFORNIA WATER NEWS: WATERSHEDS - 10/1/08

Department of Water Resources

California Water News

A daily compilation of significant news articles and comment

 

October 1, 2008

 

3. Watersheds –

 

Mosquitofish defend against West Nile, but also munch protected amphibians

San Jose Mercury News – 10/1/08

By Lisa M. Krieger

 

The scrappy little mosquitofish has been our champion in the fight against the insect-borne West Nile virus.

But for local amphibians, already struggling to survive, it is something else entirely.

 

Scientists have learned this pit bull of ichthyology has an insatiable appetite for tadpoles — including those of the threatened red-legged frog and the endangered Santa Cruz long-toed salamander. That has sent biologists draining ponds in an attempt to evict the fish; in one San Jose pond, the frog returned this spring.

The voracious guppy-like fish, which consumes an estimated 500 mosquito larvae a day, is the foundation of local mosquito control programs. It is so effective that Santa Clara County Vector Control buys it by the hundreds of pounds each year, then distributes it to residents for free to use in their backyard pools and ponds.

Given its effectiveness, environmentalists say it's impractical to ban the non-native fish, though the state has prohibited releasing it into wild waters where protected creatures live.

 

"Frog populations have disappeared from a lot of the places where fish were introduced,'' said University of California-Davis biologist Sharon P. Lawler, who has studied the problem.

 

Fish are just one of many assaults against the amphibians, which have declined because of disease, habitat destruction, pesticide use, pollution and other invasive species like bullfrogs and crayfish.

 

But the mosquitofishes' appetite is alarming. They eat almost anything that doesn't eat them first.

 

University of California biologist Jeff Wilcox, steward of the San Jose-based Blue Oak Ranch Reserve, described picking up some tadpoles and tossing them into a stream: "The mosquitofish swarmed them like a school of piranhas and tore them into bits in a matter of a few seconds.''

What they can't eat, they harass. Studies show that tadpoles in ponds with mosquitofish suffer greater injuries and weigh 34 percent less than their fish-free counterparts.

 

The fish, introduced to California in the 1920s, is a remarkably hardy creature, able to survive places that few other fishes would tolerate. And because they are omnivores, they forage through the winter after mosquitoes are long gone, so do not have to be resupplied every year.

 

"It's a terrific tool, in the right circumstances. It's biological control. It means we use fewer pesticides,'' said Santa Clara County Vector Control director Tim Mulligan.

The fish has become established over the decades, environmentalists say, and it would be infeasible to ban it.

 

Ridding a pond of fish is a big effort, said Jeff Alvarez of The Wildlife Project, which works with local water districts to eliminate the fish.

First the pond is drained, then each fish must be caught. The fragile amphibians are captured and moved into an artificial pool. Weeks later, once the pond is refilled, they're returned, Alvarez said.

 

Biologists have drained four ponds in San Jose's Blue Oak Ranch Reserve and 15 ponds in Contra Costa County. But at other locations, such as ponds on private property or large bodies of water like Los Gatos and Guadalupe Creeks, they can't be easily dislodged. Many frogs have moved into artificial stock ponds when their natural habitat is destroyed, making them vulnerable to mosquitofish that have been added to patrol those same ponds.

 

The U.S. Fish and Wildlife Service tries to control invasive species by stopping the interstate transport of the fish — but that doesn't remedy a problem caused by an already established species, said agency spokesman Joshua Winchell. The agency can also intervene when a protected species' habitat is being destroyed, but that's not the case here.

 

To slow its spread into nature, Santa Clara and most other counties, following the lead of California Department of Fish and Game, two years ago banned release of mosquitofish into natural sources, such as ponds, creeks and marshes, because of its taste for fragile species. It is a violation of state regulations for private citizens to release mosquitofish in state waters without a permit.

 

But authorities acknowledge there is no oversight once the mosquitofish are distributed. They find their way there through flooding or human carelessness, say environmentalists.

 

"They can disperse,'' said Jeff Miller of the Center for Biological Diversity, an environmental advocacy group based in San Francisco. "That's the concern.''

And people unwittingly help the fishes' migration.

 

"People see a stranded fish and want to save it,'' Lawler said. "It might make sense to the individual fish — 'Please move me!' — but it could end up in sensitive frog habitat.''

 

To kill it, Mulligan recommends super-chlorinating the water. Or letting the fish dry out. Just don't flush it down the toilet or bathtub. For the sturdy mosquitofish, this is yet another possible escape route to open waters.

"Some have survived sewage treatment,'' said Mulligan.#

http://www.mercurynews.com/localnewsheadlines/ci_10603093

 

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