Dreissena polymorpha (Zebra mussel)

Animal Molluscs
Family: Dreissenidae
Classification: Prohibited

Zebra Mussels
Zebra Mussels
Mussels removed from a boat
at the Spokane Port of Entry by WSP Inspectors
Zebra & Quagga Mussels

Zebra mussels (Dreissena polymorpha) and Quagga mussels (Dreissena bugensis) are native to the Caspian Sea, and were introduced into the Great Lakes in the mid 1980’s in ships ballast water. Zebra mussels have since spread to more twenty states, and two Canadian Provinces. Because the mussels can live out of water for up to a month if they are not subjected to heat or extreme drying conditions they may be easily transported on recreational boats. They can be on aquatic plants attached to boats or trailers, or as microscopic larvae in bilges, live wells, motor cooling systems and other water systems, or attached to the hulls, especially around trim tabs, transducers, keels or propellers. Usually the zebra mussel is about the size of an adult fingernail, but can be as large as two inches, or as small as a sesame seed. Where introduced they threaten native fish and wildlife by consuming available food and smothering native species. They clog power plant and other water intakes, costing taxpayers millions.

Quagga mussels can tolerate a much wider range of temperatures and water depths than zebra mussels. They can also tolerate brackish water, and are able to thrive in areas that zebra mussels cannot. The Quagga mussel is usually light tan to almost white, with narrow strips. It is fan-shaped, and where the zebra mussel shell is flat where the two shells attach, the quagga mussel is rounded. Unlike the zebra mussel, which has a dormant season, quagga mussels feed year around. For many years the quagga mussel was not found in any inland lakes, possibly because they tend to inhabit deeper waters than the zebra mussel. However, the quagga mussel has found it’s way to Lake Mead, near Boulder City, Nevada, and in Lake Havasu and Lake Mohave on the California/Arizona border. These are very popular recreational sites – and WDFW boat inspectors have found boats from Lake Mead and Lake Havasu at fishing tournaments in Washington State. Fortunately, launch managers and National Park authorities at these areas are making certain that boats leaving there have been inspected and cleaned.

WDFW has initiated volunteer monitoring programs in several lakes and along the Columbia and Snake rivers, and requires that out of state participants in fishing contests undergo boat inspections. Washington State Patrol Commercial Vehicle Inspectors check some of the boats that are commercially hauled into the state at the ports of entry, but not all haulers are required to stop. WDFW is increasing boater education efforts, and inspections of privately hauled recreational boats being transported from out of state. It is important that recreational boaters and anglers clean their boat and equipment before moving from one waterbody to another.


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