Last modified: Tuesday, September 17, 2013

Aquatic nuisance species

New Zealand mudsnail

Potamopyrgus antipodarum

Although the New Zealand mudsnail is only three-sixteenths of an inch long, it can develop colonies of more than 300,000 mudsnails per square yard. These colonies compete for food and space needed by trout and other native aquatic organisms.

New Zealand mudsnails
New Zealand mudsnail

By decontaminating wading boots, wetted fishing equipment and boats, anglers can do a lot to help protect their favorite fishing water from this threat to Utah's fisheries.

Mudsnail history

The first discovery of the New Zealand mudsnail in North America was in Idaho's Snake River, in 1987. Since then, they have spread to several premier western trout streams, including the Yellowstone and Madison rivers.

Mudsnails were found in Utah in 2001, when snails were discovered in the Green River, below Flaming Gorge dam. Since then, they've been inadvertently moved to multiple watersheds in Utah.

A threat to Utah's fisheries

New Zealand mudsnails found in Utah are all female and reproduce asexually, which means only one snail is required to establish a new colony. They can reproduce a million young per year and are very effective at colonizing new waters.

In some locations, mudsnails compose more than 95 percent of the biomass. They dominate these areas and because mudsnails can pass through the digestive system of trout unharmed, fish accelerate their spread. Mudsnails may provide little nutritional value to fish

Initially there was fear that our native invertebrate species would suffer from competition with New Zealand mudsnail, and a spin off impact would result in depressed sport fish populations, since trout don't seem to readily eat them. Ongoing research does not currently support those earlier fears. Our near 30-year window of experience with New Zealand mudsnail in North America is far too short for a conclusion, and it would be foolish to purposely or inadvertently spread this invasive species without a full understanding of their impacts.

New Zealand mudsnails
Greatly enlarged New Zealand mudsnail

New Zealand mudsnails also have a hard shell, with a protective operculum that closes the shell when the snail encounters adverse conditions. This makes them difficult to kill and hardy enough to survive for as long as 53 hours out of water. Their small size also makes it easy for snails to be unseen and inadvertently moved from water to water on angler's gear.

What anglers can do

Since fish do eat New Zealand mudsnail and the snails pass through the gut without being harmed, don't discard the entrails of cleaned fish into a water body from which the fish did not originate.

New Zealand mudsnail (and other aquatic invasive species such as whirling disease, didymo and likely chytrid fungus) are known to become lodged within the felt soles of wading shoes. The felt does not easily dry nor is it easily decontaminated due to the felt's dense matt; felt-soled waders support aquatic invasive species for a long period of time. Thus, anglers are advised to not use felt-soled wading shoes—suitable non-felt-soled wading shoes that are competitively priced are readily available and easily decontaminated.

Anglers can also avoid moving New Zealand mudsnail by decontaminating their wading boots or shoes and other wetted fishing equipment, including boats. Decontamination of boats is a well-known practice amongst boaters and anglers, and the recommended process will decontaminate wading boots and shoes.

Unfortunately, professional decontamination equipment is not readily available to stream anglers. So, decontamination of wading boots or other wetted fishing equipment may take an additional step or two as compared to boats, since the snails frequently lodge beneath any shoe's lacings.

First, before leaving a water body, scrub your wading boots and wetted equipment with a stiff bristled brush to remove debris and any unseen New Zealand mudsnail—remove shoe laces and spread open the tongue to expose trapped material. Then repeatedly spray your equipment with Clorox® brand 409 disinfectant, keeping the equipment damp for 10 minutes. The Clorox® brand 409 disinfectant product contains a Quaternary Ammonium compound that kills New Zealand mudsnail and the other aforementioned aquatic invasive species. Then let your equipment dry in the sun for an hour before re-use, allowing any unseen New Zealand mudsnail time to die.

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