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US Fish & Wildlife Service FieldNotes
Service and State Biologists Chase Invasive Snails
Region 8, June 29, 2010
Closeup of a New Zealand mudsnail.   (D.L. Gustafson/USFWS)
Closeup of a New Zealand mudsnail.   (D.L. Gustafson/USFWS) - Photo Credit: n/a
New Zealand mudsnails snails on penny.  (Courtesy photo/Billings Gazette)
New Zealand mudsnails snails on penny.  (Courtesy photo/Billings Gazette) - Photo Credit: n/a
New Zealand mudsnails on the seam of a wading boot. Unintentional transport from one stream location to another by hitchhiking on waders or wading boots is one of the primary vectors for spreading New Zealand mudsnails. (Jane and Michael Liu/USFWS)
New Zealand mudsnails on the seam of a wading boot. Unintentional transport from one stream location to another by hitchhiking on waders or wading boots is one of the primary vectors for spreading New Zealand mudsnails. (Jane and Michael Liu/USFWS) - Photo Credit: n/a

By J.D. Wikert and Louanne McMartin, Stockton FWO

Staff from the Stockton Fish and Wildlife Office partnered with California Department of Fish and Game biologists to survey the lower Stanislaus River from Goodwin Dam to Caswell State Park, near Ripon, Calif., in an effort to assess the spread of invasive New Zealand mudsnails (Potamopyrgus antipodarum). The invasive mudsnails were found in low densities at every site along the river that we surveyed. 

These tiny invasive snails have the ability to radically alter food web dynamics by displacing herbivores and detritivores in aquatic systems. The snails can reach high densities of over 400,000 snails per square meter and are tolerant of a variety of salinities and temperatures and have an operculum (door) that they can close, allowing them to resist desiccation and digestion.  The known U.S. populations are found in Western states and around the Great Lakes.  The New Zealand mudsnail populations in the West are self-reproducing brooders meaning they clone themselves and retain the embryos inside their shell until they are large enough to release.

New Zealand mudsnails are easily transported by recreationists and agency field crews as snails easily become lodged in crevices in waders, boot soles, nets and other items and can live for weeks in damp, cool conditions.

In an effort to stem the spread of these aquatic invaders, 17 signs were posted at various state and federal access points along the Stanislaus River, warning people about the snails and sharing information on how to prevent the spread of the snails into other waters.  The best method to prevent transporting these invasive snails to other waterways is to freeze shoes, waders, and any other equipment  for at least 6 hours at 26° F (-3°C) or below.

Please be on the lookout for New Zealand Mud Snails in your watershed, and report any suspected New Zealand mudsnails to your FWS Aquatic Invasive Species Coordinator at http://www.fws.gov/fisheries/ans/ANSContacts.cfm.

Contact Info: Paul Cadrett, 209-334-2968 x 312, paul_cadrett@fws.gov