PSU Researchers Track New Zealand Mudsnail to Deschutes River
Author: David Santen, Office of Marketing and Communications (503-725-8789)
Posted: October 24, 2005

New reports from the lower Deschutes River and the Oregon coast show that the tiny but highly invasive New Zealand mudsnail, also known as Potamopyrgus antipodarum, continues to increase its foothold in Oregon.

The popularity of these destinations among outdoor enthusiasts from around the United States heightens concern for the further spread of New Zealand mudsnails (NZMS) throughout Oregon.

Several weeks ago, Mark Ernes, Oregon State Parks ranger’s aide, reported a possible NZMS at a Deschutes River State Park boat ramp, a short distance upstream from where the Deschutes empties into the Columbia River. Based on the sample Ernes provided, Portland State University’s (PSU) Center for Lakes and Reservoirs confirmed Ernes’ report, documenting snails at Heritage Landing at Deschutes River State Park and 40 miles upriver outside Maupin, a popular fly-fishing and rafting destination. This is the first recorded presence of NZMS in this important recreational area.

“Just a couple days before I spotted the snail, a couple of people from PSU were in my area handing out the NZMS identification cards. I was amazed at the size of the snail in relation to a penny. They are such a small critter they don’t easily jump out at you,” said Ernes.

“I stopped to talk to a boater who happened to be pressure washing his gear. I looked down into the run off and saw what looked like the snails I saw on the ID card. I picked it up and rolled it around in my fingers, took out my snail ID card and called the hotline they had listed. I have a personal reason for reporting things like this. I’m an avid fisherman and I don’t want something like this where I like to fish,” said Ernes.

Robyn Draheim, assistant aquatic nuisance species coordinator at Portland State University’s Center for Lakes and Reservoirs, said that “mudsnail populations in the Deschutes are not yet as abundant as in other rivers, but they already occupy a considerable length of the river.”

Earlier this summer, new surveys and earlier collections from coastal Oregon revealed that NZMS are prevalent in the lower Rogue River, New River, and Umpqua River. New Zealand mudsnails also have been found in Garrison Lake, Floras Lake, Devil's Lake, and Coffenberry Lake on the coast, as well as in the Columbia River estuary and the Snake River.

As their name implies, NZMS are native to New Zealand. Discovered in the 1980s in Idaho, they have spread quickly throughout the West. NZMS only average 1/8” in length, but they can reach densities of over 50,000 per square foot. NZMS reproduce by cloning, so just one snail can start a new population. In fact, most of the NZMS found in the West appear to be genetically identical females. They can live in many aquatic habitats, ranging from mountain streams to estuaries. Equipped with a "hatchdoor" called an operculum, NZMS can seal their shells closed, allowing them to survive for days out of water and withstand hostile conditions.

Adverse impacts for the Deschutes River and other Oregon watersheds are still unknown. At high densities, NZMS can literally carpet some riverbeds, threatening the health of native aquatic life by competing for space and nutrients. Given their small size and ability to close their shell, NZMS offer poor food value for fish and can even pass through their digestive systems alive.

“Like most invasive species, once NZMS have become abundant in a watershed, it is extremely difficult to eradicate them,” said Paul Heimowitz, Fish and Wildlife Service ANS coordinator for the Pacific Region

It is not known how NZMS arrived in Oregon, but potential pathways include fish hatcheries, boaters, watershed survey crews, and anglers. Because the snails are so small and can survive out of water for days, they can easily hitchhike in wading boots, boats and other gear.

“Although new sightings of this invasive species are disappointing, there are many watersheds in the Pacific Northwest where NZMS have not been discovered, and their spread is not inevitable,” said Dave Allen, director of the Fish and Wildlife Service’s Pacific Region.

Individuals can help prevent expansion of the NZMS invasion by:
• Thoroughly inspecting and cleaning outdoor recreational gear, such as boots, nets, boats and trailers before leaving an area. Remove any plants, mud, or other material that may be attached. Drain all water from your boat or other watercraft (livewell, cooling system, etc.). Studies have also shown that NZMS can be killed by completely drying gear for 48 hours; freezing gear for at least 3 hours; or soaking gear in hot water (at least 120 degrees). Gear also can be cleaned by soaking them in a 50-percent solution of Formula 409 and water for five minutes.
• Reporting new sightings of NZMS and other invasive species to the Oregon Invasive Species Council hotline: 1-866-INVADER (toll-free in Oregon). Prompt detection and rapid response to new invasions greatly increases the opportunity for successful eradication.
• Getting involved in efforts to prevent introductions of other invasive species in Oregon by visiting the Oregon Invasive Species Council ( and Portland State University’s Center for Lakes and Reservoirs ( websites.

A number of groups are conducting research on strategies to fight the NZMS invasion. The U.S. Fish and Wildlife Service is leading development of a national NZMS management plan that can lead to new funds for prevention and control. Portland State University’s Center for Lakes and Reservoirs will continue to implement Oregon’s Aquatic Nuisance Species Management Plan and coordinate monitoring of state waters for NZMS and other invasive species. For more information about NZMS, including how to identify them, visit

The Center for Lakes and Reservoirs at Portland State University provides technical assistance, education, and research on management of lakes and reservoirs with an emphasis on management of aquatic invasive species. Ongoing projects at the center include management of aquatic weeds in Oregon lakes, reservoirs, drainage and irrigation canals; monitoring and outreach on mitten crabs and zebra mussels; coordination of the volunteer Oregon Lake Watch monitoring program; and nutrient criteria development for lakes in the Pacific Northwest.

The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 95-million-acre National Wildlife Refuge System, which encompasses 545 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 69 national fish hatcheries, 64 fishery resources offices and 81 ecological services field stations. The agency enforces federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign and Native American tribal governments with their conservation efforts. It also oversees the Federal Assistance program, which distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies.

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Paul Heimowitz, Aquatic Invasive Species and Research Coordinator,
U.S. Fish and Wildlife Service

Robyn Draheim, Assistant Aquatic Nuisance Species Coordinator,
Portland State University Center for Lakes and Reservoirs

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