New Zealand Mudsnail Surveys at Lower Columbia River Basin National Fish Hatcheries 2008

The New Zealand mudsnail (Potamopyrgus antipodarum) is an aquatic snail species naturally occurring in New Zealand and nearby islands. However, during the last 150 years the New Zealand mudsnail has been introduced to other parts of the world including the United States (U.S.). In the U.S., the New Zealand mudsnail was first documented in south‐central Idaho in the Snake River system in 1987 by D.W. Taylor near Hagerman, Idaho during summer mollusc surveys in The Nature Conservancy’s Thousand Springs Preserve adjacent to the Upper Salmon Falls Dam impoundment (Bowler 1991). Although speculative, the origin of these New Zealand mudsnails is likely commercial movement of aquaculture products such as trout eggs or live fish from Australia or New Zealand.

In 2002, the New Zealand mudsnail was first discovered at a National Fish Hatchery (Hagerman National Fish Hatchery in Idaho). With this discovery, New Zealand mudsnails became a new management issue for National Fish Hatchery (NFH) managers because hatchery fish transplants are a potential mechanism by which to spread the invader (Aitkin 2006). Bowler and Frest (1992) state that the occurrence of New Zealand mudsnails in Idaho’s middle Snake River basin, makes transplanting trout or other species outside the sub‐basin risky.

Regarding hatchery effluent, generally depressed populations of native snails exist downstream of fish hatcheries; however, in some Snake River tributaries, dense populations of New Zealand mudsnails exist in the waters downstream of aquaculture facilities (Bowler 1991). Frest and Bowler (1993) noted the New Zealand mudsnail “appears to build larger populations in polluted mainstem river settings or below fish hatcheries on tributaries and is less prolific in springs above pollution sources”.