New Zealand Mud Snails Invade More Rivers

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The invasion of New Zealand Mud Snails (Potamopyrgus antipodarum) began in the Snake River in 1999 which has it's source in Yellowstone National Park and then flows through Wyoming, Idaho, Oregon and Washington.

From that starting point the tiny invertebrates were next found on the Owens River in California. From the Owens River they have now nearly crossed the State and were recently found in the Calaveras River in the Mother Lode area.

The very small snails are an extremely prolific species, which are easily spread by fisherman on their fishing gear if not cleaned properly. The mud snails aren't just an invasive species though, they also supplant the native species and degrade the river ecosystem.

The New Zealand Mud snail is so pervasive in some areas of the Lower Calaveras River that during a recent study the California Dept of Fish & Game (CDF&G) found sections of the river bed which were entirely carpeted by the tiny creatures. In suitable habitats the snails can develop to a density of up to 100,000 /m2 and in sections of the some of the Yellowstone rivers the snails have reached densities of as much as 750,000/m2.

The NZ mud snail measures only about a quarter of an inch across and is capable of starting a new population with only one transplanted snail since the females begin life with embryos already "onboard"

The NZ Mud snails don't even mesh in the food chain of the rivers they inhabit, since they can live in a fishes stomach for up to three days and then be excreted still alive and none the worse for their journey. Which of course means the fish have gotten no food value from them and as a result there is also pressure on the fish populations which would normally depend on insects for all or part of their diet.

One question being posed has been what effect has the Mud Snail had on the river salmon population, their feeding habits, and the nutritional intake during the all important time before they head out to sea. The question at this point has no answer, but certainly the problem is important to the entire West Coast salmon fishery.

The CDF&G has signs posted throughout the state regarding how to deal with prevention, and nearly half of the fisherman contacted by F&G patrols are aware of the problem.

Due to the sheer volume of the infected waterways and the impossibility of eradication of the Mud snails, there is at this time no plan for dealing with the infestation other than to try to control the spread by best practises of cleaning all gear which comes in contact with an infected waterway.