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New Zealand Mudsnail

Potamopyrgus antipodarum

What is it?

New Zealand Mudsnails are relatively small (average length of 4-5 mm in western USA), with a maximum of 11 mm in native habitats. They reach maturity at 3 mm in length in rivers in western Montana and Idaho and parts of Colorado. Their shell usually consist of a right-handed coiling of 5-6 whorls. The shell varies in color (gray, light to dark brown). An operculum (i.e., plate) covers the opening of the shell. New Zealand Mudsnails have triploid, parthenogenetic female populations: asexual females are born with developing embryos in their reproductive system. Diploid, sexual male and female populations are extremely rare in western USA. Asexual females generally produce twice the number of daughters as sexual females. The adult New Zealand Mudsnail may easily be confused with various native and exotic species which can be similar in appearance, and all newly discovered populations should be verified by experts. The shell of the New Zealand mud snail is narrower, longer, and has more whorls than most hydrobiid snails native to the United States. New Zealand mud snails are live bearers (they release embryos and not eggs), and therefore, the presence of newly released young may indicate a possible population. New Zealand mudsnails can inhabit lakes, ponds, streams, rivers, lagoons, estuaries, canals, ditches, water tanks, and reservoirs and occupy a wide variety of substrates including silt, sand, mud, concrete, vegetation, cobble, and gravel. They are capable of tolerating a wide range of temperatures with upper thermal limits of 28°C and lower thermal limits near freezing. The also have a wide salinity tolerance range from saline and brackish to freshwater. Populations in saline conditions produce fewer offspring, grow more slowly, and undergo longer gestation periods. Individuals of this species are able to tolerate turbidity, clear water, and degraded conditions (including sewage and may pass through the digestive tracts of many fish species.

 

Why is it a problem?

The New Zealand Mudsnail has a history of becoming a pest species in many parts of the world and its introduction into Colorado waters is cause for concern. Streams are rapidly becoming infested as populations continue to grow. These small snails have the ability to displace native Colorado invertebrates. Their establishment will have negative impacts on native fauna and plants close to water sources. There is growing evidence for a decline in populations of mayflies, stoneflies, caddisflies, and chironomids where New Zealand Mudsnail have become established. This species also has the potential to impact the food chain of native Gunnison valley trout and other fish species. The snail has the potential to wreak havoc on many of the Gunnison valley ecosystems that already face invasion from other invaders. Once established in reservoirs they have been known to emerge from water taps as they make their way through the water system.  

 

Management Techniques:

  • Subjecting this species to heat, desiccation, and hard freeze will kill them.

  • A trematode native to New Zealand may be of assistance in the development of a biological control, but further research is needed.

  • NPS and CPW continue to monitor river, lakes and reservoirs in hopes of keeping the New Zealand Mud snail at bay.

 

What can we do?

Transportation is believed to occur mainly via contaminated equipment of recreational boaters and anglers, and therefore, the following will assist in containing the spread: Scrub and thoroughly rinse boat, gear, and equipment before exiting an infested area. Allow everything to dry in low humidity for at least 24 hr before entering another body of water. Scrub and thoroughly rinse off all mud and debris (e.g., aquatic vegetation) which may be adhering to boots, waders, clothing, etc. before leaving an infested area. Allow to dry in low humidity and high temperature > 30 ºC for at least 24 hr before entering another body of water.

 

Entities working on this invasive in the Gunnison Basin:

Bureau of Land Management 

This link discusses how the BLM’s Fisheries Program addresses the threat of the mudsnail by working with counterparts in State and other Federal agencies through the national interagency Aquatic Nuisance Species Task Force and its Western Regional Panel.

 

General Information on New Zealand Mudsnail:

Forest Service

This is the Forest Service/Interagency guidance on how to handle aquatic invasive species.

 

National Park Service

  • This link discusses the issue the mudsnail has caused in Yellowstone NP and how NPS approached the situation.

 

Aquatic Nuisance Species Task Force

  • A website for ANS Task Force's national management plan

 

United States Geoogical Survey

  • Website on identification and management of New Zealand Mudsnails

 

Colorado Parks and Wildlife

 

 

 

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