Invasive New Zealand mud snail confirmed at three Skagit County locations putting fish and others at risk

(SKAGIT COUNTY)- The highly invasive New Zealand mud snail has been confirmed at three locations in Skagit County. The snails were first discovered by the Washington State Department of Agriculture in late 2018 while doing water quality monitoring at Big Indian Slough, and again in August and September of 2019 at Carpenter Creek and Joe Leary Slough by Skagit County water quality monitoring staff and members of the Skagit Drainage & Irrigation Consortium. County water quality officials are encouraging extra precautions to prevent the further spread of these harmful invaders.

“We strongly encourage anyone who works, fishes, or otherwise recreates in ditches, streams, or other waterways in Skagit County take special care to decontaminate their gear before leaving the site, whether or not they see evidence of mud snails,” said Michael See, Skagit County’s Natural Resources Division Manager. “The snails are very small and can be difficult to see. Preventing their spread is paramount.”

The invasion of New Zealand mud snails is harmful to local ecosystems for a number of reasons. New Zealand mud snails can spread very quickly, and rapidly outcompete native macroinvertebrates. (Examples of macroinvertebrates include segmented worms, mayflies, stoneflies, caddisflies, mollusks, and leeches.) These macroinvertebrates are a primary source of food for fish, including juvenile salmon. While fish can safely eat New Zealand mud snails, fish are unable to digest the snails due to their hard exterior and eventually become malnourished.

“There are chemical treatments that can kill New Zealand mud snails, but none are appropriate to use in open water systems,” said Jesse Schultz from the Washington Department of Fish and Wildlife’s (WDFW) aquatic invasive species unit. “To my knowledge, there has never been a successful eradication of New Zealand mud snails in an open water system. New Zealand mud snails are most likely to spread through human activity such as boating, fishing, surveying, and construction work. That’s why WDFW’s primary management strategy for New Zealand mud snails is to prevent the spread by humans by classifying them as a prohibited species and urging people to decontaminate their equipment.”

To help prevent the spread of New Zealand mud snails and protect the delicate balance of local ecosystems, including the primary food source for the many fish species that live in our local rivers, basic decontamination should be done after all water-based activities on Skagit County waterways, regardless of a confirmed presence of New Zealand mud snails. Basic decontamination includes scrubbing all gear and rinsing with potable water to remove any debris while still at the site. At sites where New Zealand mud snails are present, decontamination procedures should include soaking gear in water that is at least 140°F. Porous gear should be soaked for a minimum of five minutes. Hard, non-porous gear should be soaked for a minimum of 15 seconds. Exposure to freezing temperatures between 14°F to 32°F (-9°C to 0°C) for at least 24 hours will also kill New Zealand mud snails.