The Colorado Division of Wildlife is asking for the public’s help in containing aquatic exotic species’ that have the potential to harm the state’s fisheries. One species of particular concern is the New Zealand mudsnail.“The mudsnail has the potential to devastate Colorado’s fisheries and harm native fish species,” Gary Skiba, multi-Species Coordinator for the Colorado Division of Wildlife (DOW), said. “Our goal is to get the word out about this exotic so the public is not only alerted to the threat, but will also be proactive in preventing its spread.”

New Zealand mudsnails (Potamopygus antipodarum) are native to the freshwater lakes and streams of New Zealand. Only 1/8-inch long, they were first detected in the United States in the mid-1980’s when they were found in the Snake River region of Idaho. They have since spread to Montana, Wyoming, California, Arizona, Oregon and Utah, including several waters in Yellowstone National Park. The only known population in the eastern U.S. is in Lake Ontario, where a population was discovered in the early 1990’s.

Currently there is a reported, but not documented, population of mudsnails on the Green River in Colorado, just over the Utah boarder. Studies are being conducted to find out if the exotic has reached any other Colorado waters, according to Pete Walker, senior fish pathologist for the DOW.

The biggest threat posed by the mudsnail is its ability to compete for food and eventually displace resident invertebrates – e.g. bugs that feed fish. Lack of natural predators and the snail’s ability to reproduce asexually have led to densities as high as 750,000 for every 10.7 square feet of river bottom. To put it in perspective, every day Idaho Power has to remove 15 tons of snails that are as small as a grain of sand from their trash racks to prevent clogging the Middle Snake River Dam.

While there is potential for mudsnails to impact the food chain for native trout, research is still being conducted on how destructive the snails are to native fauna such as aquatic insects and native snails. Preliminary studies indicate that the mudsnails may be impacting the invertebrate community in the Madison, Firehole and Gibbon rivers in Wyoming and Montana.

Not only do these streams support world famous fisheries; they also contain an abundance of native aquatic insects that are an important part of the food chain. Mudsnails are a poor substitute for this traditional food base, yielding as little as 2 percent of their nutritional value when eaten by trout. Often they pass right through the trout and other fish without being harmed.

The snails can survive several days out of water, can withstand a wide range of temperatures and are small enough to be inadvertently spread by many types of water users. All waters are vulnerable, from silted river bottoms to clear mountain streams. Since the snails reproduce asexually, it only takes one attached to fishing gear, watercraft, pets, clothing or anything else that came in contact with water to spread them. The transfer of fish and bait can also introduce the snails to previously uncontaminated water.

“Making sure equipment is clean and that every possible precaution has been taken to prevent the spread of different aquatic exotics is part of being a responsible angler and an ethical sportsman,” Skiba said. “We need the cooperation from the public if we want to help stop the spread of harmful exotics.”

Anglers and others who recreate around water are asked to take some simple precautions. Make sure waders and other equipment has been completely dry for an extended amount of time before visiting other waters. Wash equipment that has been in contact with water with a bleach solution to kill any possible exotics that may have attached themselves. Inspect boats and watercraft and remove any residual water or vegetation before putting into new waters.

For photos of the New Zealand Mudsnail contact Tyler Baskfield.