Update: New Zealand Mud Snails

Update: New Zealand Mud Snails

New Zealand mud snails are here to stay, and they are spreading.

New Zealand mud snails are here to stay, and they are spreading. That's the bottom line from scientists and conservationists who monitor these tiny invasive organisms. First observed on Idaho's Snake River in 1987, the mud snails are now established in many of the West's best trout rivers--including the Madison, the Yellow-stone and, most recently, Piru Creek in southern California.

New Zealand mud snails present two main problems to river ecosystems: First, they are prolific breeders. Once established in a river they can reach densities as high as 200,000-500,000 per square meter, which means that by sheer numbers alone, they out-compete other aquatic invertebrates such as immature insects for nutrients. The second problem is common to most exotic invasive species: They have no natural predators in North America, which allows them to colonize a river unmolested.

It is no coincident that the mud snails are present in some the finest trout rivers in the country, as fly-fishermen are one of the leading vectors (along with other river users such as kayakers and rafters) spreading the snails from river to river.

According to Bob Wiltshire, the Federation of Fly Fishers' invasive species coordinator, "The only way to deal with mud snails is prevention. As anglers we have to do everything in our power to not move them from one river to another."

That is easier said than done, of course. New Zealand mud snails are tiny (less than a quarter of an inch long), which is small enough to be missed even during a close inspection of boots and gear. They are also hard to kill. The most effective way yet discovered to eliminate the snails from waders and other gear is a 50-50 solution of water and Formula 409.

According to preliminary studies (this application is currently undergoing formal peer review), the treatment leads to 100 percent mortality ONLY if the items are allowed to soak for five minutes. Simply spraying your boat or waders with the stuff won't do the trick; items must be soaked.

Unfortunately, the best anglers can do is prevent the snails from spreading to more watersheds; there isn't a way to eradicate them where they are already established. FFF recommends the following checklist for anglers to control the spread of mud snails (and all invasives for that matter):

Wash your gear and pay particular attention to boots.

Clean all debris off your boat and trailer.

Drain boat at boat ramp.

Thoroughly dry equipment.

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