New Zealand mudsnails found in the Duluth-Superior Harbor.
New Zealand mudsnails on a penny to show size
Species and Origin: A tiny snail that reproduces asexually. Native to New Zealand, it was accidentally introduced with imported rainbow trout in Idaho in the 1980s and into the Great Lakes via ballast water from ocean going ships.
Impacts: Densities can reach 100,000 to 700,000 per square meter. They outcompete species that are important forage for native trout and other fishes and provide little nutrition to fish that eat them.
Status: First discovered in the late 1980s in the Snake, Idaho, and Madison Rivers, they quickly spread to other western rivers. They were discovered in Lake Ontario, and later in Thunder Bay, Lake Superior in 2001. In fall of 2005, they were discovered in the Duluth-Superior harbor. See US map .
Where to look: Look on docks, rocks, and other hard surfaces along the shorelines and bottoms of lakes, rivers, and streams.
Regulatory classification (agency): It is proposed as a prohibited invasive species (DNR), which means import, possession, transport, and introduction into the wild will be prohibited.
Means of spread: They likely spread by attaching to recreational fishing gear, other types of equipment placed in the water, or in fish shipments.
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