Slowing the snails’ pace

Davis Enterprise - December 05, 2006
By Barry Eberling

Slowing the snails’ pace
Davis Enterprise – 12/06/06
By Barry Eberling, McNaughton Newspapers

FAIRFIELD — Ken Davis scooped a net into Putah Creek, searching for New Zealand mud snails that could make fish populations plummet and someday cause problems at water treatment plants serving local cities.

As expected, his net contained hundreds of tiny, black snails.

Davis, an aquatic biologist, has tracked the spread of the snails along Putah Creek for three years. He’s seen the non-native creature move from a spot near Monticello Dam downstream some 15 miles, almost to Pedrick Road. The snails come to a new stretch of creek and swiftly colonize it.

“Where they were last year, there’s a lot more,” Davis said.

This creature the size of an aspirin is nothing but a headache. But there is hope the mud snail doomsday scenarios for Putah Creek may yet be avoided — and people such as Davis are looking for the answers.

Putah Creek forms the border for Solano and Yolo counties. It winds from Lake Berryessa reservoir through rich farmland to Davis and the Yolo bypass.

New Zealand mud snails — native, of course, to New Zealand — first appeared in the United States about 20 years ago in Idaho’s Snake River. The snail can live for days in a damp fishing boot and only one snail is needed to reproduce. It has no natural enemies locally.

Davis speculates that somebody fishing brought the snail to Putah Creek. He discovered them there in October 2003.

Mud snails eat algae that are food to mayflies and caddisflies, which in turn are food to fish. The snail can disrupt the food chain and cause fish populations to crash.

Davis has seen a drop in mayflies in some areas of the Lake Solano portion of Putah Creek. Mayflies are a major trout food.
“To me, it’s a red flag to look a little closer,” Davis said.

Some parts of the creek have up to 300,000 to 500,000 snails per square yard, Davis said. The goal is to keep the numbers down to 25,000 per square yard, so the snail population is manageable.

The snails don’t like areas with fast water, Davis said. Creating areas with quicker flows is one potential way of controlling the mud snail population.

Rich Marovich tends Putah Creek for the Lower Putah Creek Coordinating Committee. He and the committee have plan to create faster flows in some areas, not only to deter snails, but to help salmon.

Marovich also sees potential for introducing mud snail enemies into the creek, though that day is far away. For example, he said, the mud snail population is controlled in New Zealand by a parasite that sterilizes the snail.

Meanwhile, Marovich is among those keeping a close eye on the creek.

“The jury is still out on the ultimate effect of the snail,” Marovich said.

Mud snails have also spread from the creek into the concrete-lined Putah South Canal that brings drinking water to Fairfield, Suisun City, Vacaville and other cities. Should the snails ever reach the water treatment plants, they could clog up intakes and interrupt water treatment.

“We’re not sure whether that can happen,” said David Okita, general manager for the Solano County Water Agency. “We don’t know. There hasn’t been any infestation that are in a situation like ours ... every other outbreak we’ve seen in the USA has been in a natural stream.”

The snail has spread into the concrete-lined canal for about 2.5 miles of its length, Davis said. The water treatment plants are still several miles away.

“We’re kind of in an unknown world,” Davis said. “To my knowledge, they’ve never been in a water conveyance system before.”

The state Department of Fish and Game is looking at ways to control the snail in the canal, Okita said. There must be a balance between killing snails and not harming drinking water, he said.

Water officials already put copper sulfate into the canal to kill algae, Marovich said. That can be toxic to snails, he said.

While Marovich is a mud-snail foe, he also sees a side to the invasive species that impresses him.

“To go from not even being detectable to covering the floor of the creek in some areas with these very high densities — it’s hard to even imagine that kind of increase,” Marovich said.

But it’s happening. Now Putah Creek advocates and water officials must find a way to kill the mud snail or live with it. #
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