With the Dec. 1 opening of steelhead trout fishing in coastal counties south of San Francisco, the California Department of Fish and Wildlife reminds anglers that it's critically important to clean gear after every fishing outing.

This practice helps prevent the spread of New Zealand mudsnails (NZMS), tiny (3/16") aquatic snails capable of surviving out of water in the crevasses of damp gear for weeks.

The resiliency of NZMS has enabled them to spread to aquatic environments across the globe, including Europe, Australia, North America, and Asia.

To prevent further spread, anglers and others who wade or work in California waters should thoroughly clean all gear before using it in another waterbody.

"While New Zealand mudsnails have been detected in watersheds across the state, many watersheds and counties remain free of this unwanted species. Anglers and the public are key to keeping these waters free of mudsnails," said CDFW Senior Environmental Scientist George Neillands.

NZMS were first reported in California in 2000 in the Owens River (Inyo and Mono counties).

In 2003, NZMS were discovered in northern California in Putah Creek (Yolo County) and the Mokelumne River (San Joaquin River).

They have since been detected in one or more waterbodies in 27 additional counties: Alameda, Butte, Calaveras, Contra Costa, Del Norte, Glenn, Humboldt, Los Angeles, Marin, Mendocino, Merced, Monterey, Napa, Orange, Sacramento, San Luis Obispo, San Mateo, Santa Clara, Santa Cruz, Shasta, Siskiyou, Solano, Sonoma, Stanislaus, Tehama, Ventura, and Yuba.

NZMS can survive in a variety of environments including rivers, streams, reservoirs and estuaries. They are parthenogenic live-bearers, meaning they self-reproduce. This enables a new population to begin from only one snail.

NZMS have demonstrated the potential to reach high densities of up to nearly one million snails per square meter and comprising up to 95 percent of the invertebrate biomass of a river.

When they reach high densities, NZMS outcompete native insects and invertebrates for space and algae, which reduces the forage available to steelhead trout.

As a result, steelhead populations can decline. Once NZMS are established in a body of water, it may not be possible to eradicate them.

Here's what you can do to prevent the spread of NZMS:

– After leaving a body of water, inspect all gear including waders, boots and float tubes. Also inspect boats and trailers. Remove visible debris with a stiff brush and rinse on site.
– Freeze waders and other gear overnight (for a minimum of six hours) or dry completely between use.
– Use additional waders and boots in infested waters and store them separately.
– Never transport live fish or other aquatic animals or plants from one waterbody to another.

For more information on NZMS visit www.wildlife.ca.gov/NZMS .