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New Zealand mud snails found in western Montana

FWP classifies these snails as an aquatic invasive species
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Posted at 5:01 PM, Sep 24, 2019
and last updated 2019-09-24 19:01:36-04

Last month, Montana Fish, Wildlife & Parks discovered an established population of New Zealand mud snails at a private commercial fish hatchery south of Hamilton.

It marks the first time New Zealand mud snails have been found west of the Continental Divide in Montana, but populations are known to exist in Idaho, Washington, Oregon, and California.

FWP said in a press release on Tuesday that these snails are an aquatic invasive species (AIS), which, once established in a natural system, can have localized impact to aquatic ecosystems. New Zealand mud snails do well in cold water environments and are present in several water systems east of the Continental Divide including the Madison, Missouri and Yellowstone rivers.

The Bitterroot hatchery is now under quarantine by FWP, which will last until the New Zealand mud snails are eradicated from the facility.

The snails likely arrived at the Bitterroot hatchery from a fish hatchery in South Dakota, which was thought to be free of AIS until notice this summer that New Zealand mud snails had been discovered there. The Bitterroot hatchery imports trout from the South Dakota hatchery annually.

In Montana, private fish hatcheries are used to stock private ponds with fish. The hatcheries are permitted by FWP and inspected for fish disease and AIS annually. FWP hatcheries only stock private ponds that provide access for public fishing.

The Bitterroot hatchery receives annual inspections from FWP for fish disease and AIS, and New Zealand mud snails were discovered this year. The Bitterroot hatchery drains into an irrigation canal, not the Bitterroot River. FWP staff have surveyed areas of the Bitterroot River and Skalkaho Creek, both of which are near the hatchery, but have not found any invasive snails.

The FWP website has more information, including this overview:

  • First found in Montana in 1995 the Madison River, it has since spread
  • It has reached very high densities (300,000/m²) and at such densities can have significant impacts to ecology of areas it is introduced into
  • Reproduces asexually thus it only takes one to start a new population
  • Size: adults can reach up to ~ 0.15-0.25 inches in length
  • Shell if right-handed coiling, elongated with 7-8 whorls separated by deep grooves.
  • Shell colors vary from gray and dark brown to light brown.

You can also learn more about New Zealand mud snails on the Montana Field Guide website .

Aquatic Invasive Species (AIS) are defined by FWP: "AIS are introduced accidentally or intentionally outside of their native range. AIS populations can reproduce quickly and spread rapidly because there are no natural predators or competitors to keep them in check. AIS can displace native species, clog waterways, impact irrigation and power systems, degrade ecosystems, threaten recreational fishing opportunities, and can cause wildlife and public health problems."