Snails Pose Threat Via Lake Natoma Trout Hatchery

A tiny but tough and very hungry foreign snail has invaded the American River, prompting concern that waters throughout the state could become infested if it gains a foothold in the river’s trout hatchery.

The New Zealand mudsnail has been confirmed in two locations on the river this month, both below Lake Natoma. On other rivers, the snail has been known to carpet the river bottom at more than 500,000 per square meter, and it could devour food available to native fish in the river.

But officials are equally concerned about preventing the snail from being transported by human activity above Nimbus Dam and into Lake Natoma, the water supply for the state’s American River Trout Hatchery.

The tiny snail — less than 5 millimeters long — can survive in the stomachs of fish for up to three days and be excreted alive into new waters. So the millions of trout transplanted from the hatchery each year to lakes throughout the state could spread the snail far and wide.

"It’s our top priority to ensure that does not occur," said James Navicky, an environmental scientist with the state Department of Fish and Game.

"It could be a relatively simple thing to move the snail above Nimbus. We’re going to have to really step up what takes place here."

Fish and Game officials last week held an emergency meeting to discuss the problem, Navicky said, and immediately adopted new monitoring procedures to detect the snail at the hatchery.

The snail is primarily transported by attaching itself to people and their equipment, and officials urge the public to help prevent its spread.

Fishing waders, boats and other aquatic gear should be frozen overnight or vigorously cleaned and dried before moving between the lower American River and Lake Natoma or any other water body.

The snail can survive out of the water for up to a month on a boot sole or a boat’s hull. So the cleaning must be thorough.

Gary Eblen, owner of American Fly Fishing Co. in Sacramento, said this will be an uphill battle because of the "unbelievably heavy" human traffic in the American River Parkway. It is probably the most heavily populated place infested by the mudsnail in California, if not nationwide.

Signs have been posted along the river for years to warn anglers about transporting mudsnails. Yet they arrived anyway.

"You’ve got everybody and their uncle out there fishing. Some of them care. Some of them don’t," said Eblen. "Stopping it is going to be a massive and difficult effort."

The New Zealand mudsnail was discovered in the United States in the late 1980s in the Rocky Mountains. Its first California appearance came in 2000 in the Owens River, east of the Sierra Nevada.

The snail leaped the range three years later with an appearance in Putah Creek in Yolo County, and is now found in eight locations west of the Sierra.

In the American River, it was found Nov. 12 about a half-mile below Sunrise Bridge by Ken Davis, an independent aquatic biologist based in Sacramento; then on Nov. 14 at San Juan Rapids by Mike Healey, a fisheries biologist at the Department of Fish and Game.

"They are reproducing," said Davis. "Everything is there for them to prosper."

Navicky said the effect on the river’s primary native fish — salmon and steelhead — might not be severe. That’s because these fish are migratory, spend most of their time in other places, and don’t feed much when they return to spawn.

But the snails have the potential to upset the entire food chain in the river.

"It’s suspected they can have severe ecological impacts in the waters where they’re found, but that’s an area where we need more research — in the U.S. in general, not just in California," said Denise Walther, assistant aquatic invasive species coordinator at the U.S. Fish and Wildlife Service office in Stockton.

The snails are prolific and can spread quickly in a watershed. On Putah Creek, they were first found just below Monticello Dam at Lake Berryessa in October 2003, and are now throughout the creek as far downstream as Pedrick Road, a distance of more than 12 miles. Some spots now host more than 100,000 snails per square meter.

There is no practical way to eliminate the snail once it becomes established. Evidence suggests, however, that they don’t like fast water, which may help limit their spread in the American River.

If the snails enter Lake Natoma, research from other locations indicates they could be controlled by water filtering systems or new water treatment steps.

This would add expense and time to the hatchery process.

"It’s going to have an impact one way or another. It’s not good," said Davis. "At this point, rather than try and guess what’s going to happen, we emphasize that people clean their equipment no matter what river they’re in."