Invaders threaten native species

SANDPOINT — A popular fishing spot is being threatened by an unwanted intruder.

The Chinese mystery snail has invaded Round Lake in Sagle, and Idaho Parks and Recreation can only speculate how the invasive species got there. Also known as a trapdoor snail or cipangopaludina chinensis per the scientific name, the species is commonly sold online for aquariums.

“We suspect somebody dumped something from their aquarium into our lake and the snails came along with it, or they dumped the snails in,” said Mary McGraw, Round Lake State Park manager. “People don’t realize what a bad idea that really is.”

Park officials began to notice the snails a couple years ago, McGraw said, and this year the population “exploded.” Chinese mystery snails are named as such because, in the spring, they give birth to young, fully developed snails that “suddenly and mysteriously” appear, according to lakegeorgeassociation.org.

McGraw said she read that the snails can have up to 102 babies in a single brood, which explains why the numbers are growing exponentially. She also read that they thrive at 20 to 25 degrees Celsius after giving birth, which is the exact temperature of Round Lake.

“So it is the perfect environment for them to thrive, and without any natural predators and checks and balances, they just explode.”

The danger of the snails to the lake is that they eat a lot of algae, which is why they are popular for aquariums as they help keep them clean. On the other hand, when they get into a lake and eat up a lot of the algae, it leaves less food for the native species, McGraw said. There are trout planted in the lake as part of the family fishing program, as well as bass and other species that will decline as the snail population grows.

“In a small lake where you have a limited amount of food, it becomes a major issue in a pretty big hurry,” McGraw said.

To involve the community in the process of getting the snails out of the lake, as well as to create awareness of the problem, park officials recently began handing out coupons trading a free ice cream for a dozen snails, and then discounted ice cream for every dozen after that. On Monday alone, McGraw said between 500 and 800 snails were brought into the visitor center.

IDPR has been working with the Idaho Department of Agriculture on a Eurasian milfoil invasion in the lake, so they are now helping out with the snail problem as well. McGraw said she is hoping, as small as the lake is, that the plan to get rid of the invasive species will not include herbicide or pesticide. On the Eurasian milfoil project, the Department of Agriculture has done surveying of the lake over the past couple of years, she said. They identified a couple areas where the invasive species is starting to take over, so the department will be sending divers in to hand-pick the Eurasian milfoil to avoid poisoning the lake, she said.

“They (the Department of Agriculture) have been wonderful to work with,” McGraw said.

Milfoil is typically transferred from one lake to another via a boat or trailer, McGraw said, and it is possible the snails could have been introduced that way as well. There has been reports of the snails in other lakes in North Idaho as well, she said. It is important to clean boats and trailers, she said, washing them with hot water and making sure they are dry — and never get rid of aquarium pets or plants by taking them to a lake, river or other natural body of water.

McGraw said they will continue to offer one free ice cream per person for the first 12 snails brought to the visitor center, and 40-percent off for each additional 12 snails, until the ice cream is gone this season. Visitor center hours are 3-6 p.m. during the week, and 1-8 p.m. on Friday and Saturday. Round Lake State Park is located at 1880 Dufort Rd., Sagle.

Information: parksandrecreation.idaho.gov/parks/round-lake

Mary Malone can be reached by email mmalone@bonnercountydailybee.com and follow her on Twitter @MaryDailyBee.