DFG News Release

DFG Seeks Assistance in Slowing Spread of New Zealand Mud Snails

The California Department of Fish and Game (DFG) is requesting assistance from the public in slowing the spread of New Zealand mud snails (NZMS). The tiny invasive aquatic snails were confirmed last month to live in Lake Shasta and previously have been discovered in numerous bodies of water in California.

“New Zealand mud snails are just one of the many non-native invasive species that are impacting our native resources and recreational opportunities,” said DFG Invasive Species Coordinator Susan R. Ellis.

To help prevent further spread of the snails, anglers and others who frequent California waters are asked to thoroughly clean all gear that comes in contact with the water, prior to moving to another location. In addition, individuals who are visiting state fish hatcheries should be careful to remove waders that have been in contact with affected waters before entering hatchery grounds.

NZMS, which reproduce rapidly and can crowd out native insects that aquatic wildlife depend upon for survival, were first discovered in California in 2000 in the Owens River in Mono County. Other bodies of water and the counties in which they have been found include Hot Creek (Mono), Bishop Creek Canal (Inyo), Lone Pine Creek (Inyo), Medea Creek (Los Angeles), Lindero Creek (Los Angeles), Malibu Creek (Los Angeles), Solstice Creek (Los Angeles), Segunda Descheca Creek (Orange), Trabuco Creek (Orange), Piru Creek (Ventura), Putah Creek (Yolo), Lower Calaveras River (Calaveras/San Joaquin), Mormon Slough (San Joaquin), Lower Mokelumne River (San Joaquin/Sacramento), American River (Sacramento), Rush Creek (Marin), Lower Napa River (Napa), San Lorenzo River (Santa Cruz), West Antioch Creek (Contra Costa), and Alameda Creek (Alameda).    

It is believed that NZMS spread to new river systems primarily by humans, although it also is possible that wildlife plays a role. Recreationists such as anglers and boaters, researchers and others who frequent lakes, rivers and streams can inadvertently move mud snails to new locations and therefore should carefully clean their gear. For example, the snails can attach to debris and mud left on waders and survive for weeks in these moist conditions. When an angler visits a new stream the snails can deposit there.

NZMS colonies disrupt the base of the food chain by consuming algae and competing with native bottom-dwelling invertebrates. A population decline of invertebrates (small aquatic insects) can follow the introduction of NZMS, which reduces fish forage. With a decrease in food availability, fish populations can decline as well.

NZMS can grow as large as one-quarter inch but are often much smaller and are parthenogenic or able to start a new population with only one snail. NZMS have the potential of extraordinary population densities - up to nearly one million snails per square meter and comprising up to 95 percent of the invertebrate biomass of a river. It is believed that populations in New Zealand are kept in check naturally by a native parasite. In North America, however, native stream communities can be altered because the snail has no natural predators or parasites and its populations have flourished where they have been introduced. It is not believed they can be eradicated once established.

NZMS should not be confused with Quagga or Zebra mussels that first invaded North America in the Great Lakes region. Quagga mussels were found in the Colorado River in early 2007 and later in several bodies of water in San Diego and Riverside counties. Both of these species of mussels, which are native to Caspian Sea and Black Sea watersheds in Europe, are of great concern because of their ability to cause severe damage to the natural environment as well as to power plants, water supply intakes, as well as other negative impacts.

What you can do to prevent the spread of NZMS:

• Have extra waders and boots for use in infested waters only. Store them separately.
• After leaving the water inspect waders, boots, float tubes, boats and trailers, dogs and any gear used in the water.
• Remove visible snails with a stiff brush and follow with a rinsing.
• If possible, freeze or completely dry out wet gear before reuse.
• Never transport live fish or other aquatic animals or plants from one body of water to another.

For more information on NZMS and where they have been detected, visit the DFG Web site at www.dfg.ca.gov/invasives/mudsnail.