New Zealand mudsnails found in Chehalis River

New Zealand mudsnails have been found in the Chehalis River.

The mudsnails were found by Edward Johannes of Deixis Consultants, and Stephanie Clark with Invertebrate Identification Australasia, along the Blue Slough.

The mudsnails were found at the Washington Department of Natural Resources Blue Slough Access area. The snails were found in mud around a spring at the site. The New Zealand mudsnails were collected during low tide, as the site is inundated with water at high tide.

The New Zealand mud snail was first found in the Snake River in Idaho in 1987. By 1997 there was a population in the Madison River in Yellowstone Park. In some areas they were in densities of up to 750,000 per square yard. In Washington there are established populations in the Columbia River at Young’s Bay and Kalama, in the Snake River near the border in Idaho, and in a number of private waterways on the Long Beach Peninsula. They are now present in Capitol Lake in Olympia.

The Washington Department of Fish and Wildlife say that New Zealand mudsnails are small (about 1/8 – 1/4 of an inch long when full grown) that have brown or blackish cone-shaped shells with five whorls. They tolerate a broad range of temperature, salinity, and water quality, and have no natural parasites or predators in the United States. Based on a single snail and each offspring in turn reproduces itself, by year two there may be over 52,000 snails, by year three over 12 million snails, and by year four over 2.7 billion snails carpeting the bottom of a river or lake. Preliminary studies indicate that in areas where they have become densely populated they are becoming the dominant invertebrate via displacement and competitive interactions. Large populations may consume up to half of the available food in a stream, starving out insects essential to trout and salmon. A recent study by the U.S. Bureau of Land Management and the Utah State University (Vinson and Baker, 2008) linked these invasive snails to poor condition of trout due to lack of a regular food source and that the snails did not provide sufficient nutritional value when consumed. The snails are very small – between an eighth and a quarter inch in size – and may not be noticed attached to tackle, waders, boats, etc.

Additional samples were taken at the WDFW boat ramp near the SR107 Bridge as well, but no mudsnails were found.

How the species came to the area is not known.





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