Cold estimated to have killed half of snails in Capitol Lake

Officials lowered Capitol Lake earlier this month in effort to kill off invasive New Zealand mudsnail

bshannon@theolympian.comDecember 26, 2013 

In this file photo from 2010, the New Zealand mud snail is very small to see, even under a magnifying glass.

STEVE BLOOM — Staff photographer Buy Photo

The heavy cold snap earlier in December proved to be a big help to state officials trying to limit an unwelcome New Zealand mudsnail population that has infested Olympia’s Capitol Lake.

Officials lowered the lake during a weeklong subfreezing spell that saw temperatures fall into the teens five nights during the Dec. 4-9 period, and state scientists estimated that 40 percent to 60 percent of the tiny rice-sized snails were killed lakewide.

In a summary report on the drawdown experiment, the state Department of Enterprise Services called it “the most effective treatment of New Zealand mudsnails since the pest was first found there in 2009.” It cited the findings of the Department of Fish and Wildlife, which has monitored the mudsnail population and oversaw two previous efforts to kill off the tiny mollusks using the cold.

Wildlife scientist Allen Pleus carried out inspections of the lake shore before and after the latest freeze.

Pleus could not be reached for comment Tuesday, but the results appeared to match his hopes from early in December. “At the end of this if we got 50 percent mortality, I’d be really pleased. We might get higher mortality around areas that are more exposed,’’ Pleus said earlier.

DES is characterizing the results as more successful than similar efforts in 2009 and 2012.

“The Department of Fish and Wildlife conducted a limited survey and analysis of snail mortality rates during the recent drawdown,” the DES report says. “Their survey summary reported a 100 percent kill rate of the snails in three sample areas in the north basin of the lake. The survey coordinator estimates that this translates into a 40 to 60 percent overall mudsnail mortality rate lakewide, although he concedes this estimate is highly speculative.”

Enterprise Services is the state’s landlord agency and manages Capitol Lake, which is part of the state Capitol Campus.

No one knows precisely why the aquatic invasive species is in Capitol Lake, but it has been contained to the lake areas and has not spread to nearby waters. DES says “the snails are found in fresh and brackish water throughout the western United States” and reproduce asexually, which means just one snail can begin a new population.

The species is considered a problem because it interferes with the food chain, robbing fish populations that compete for the same nutrients in the water.

Brad Shannon: 360-753-1688 @bradshannon2

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