Tiny Invasive Snails Confirmed At Lake Sonoma Fish Hatchery

SONOMA COUNTY, CA — State officials have confirmed the presence of invasive New Zealand mudsnails at Warm Springs Fish Hatchery near Lake Sonoma and are asking people who go fishing and boating in the watershed to take certain precautions.

The mudsnails were previously detected in other parts of the Lake Sonoma watershed but it is the first time they were found at the facility where Coho salmon, a federal and state-listed endangered species, and steelhead, a federally-listed threatened trout species, are produced and released, the California Department of Fish and Wildlife said Friday in a news release.

Dense populations of the invasive snails can displace and out-compete native species, consuming up to half of the food resources in a stream. They've also been linked to reduced populations of insects — mayflies, caddisflies and chironomids, to name a few — that are important to trout and salmon.

The invasive snails were initially detected over the summer in an intake pipeline and an aeration pond during a regularly scheduled quarterly hatchery. Since the detection, scientists have conducted surveys in about 75 percent of Coho-bearing streams in the watershed and have not observed their presence beyond previously known locations. The surveys were focused on stocking locations for Coho and steelhead species, which take place mostly in Russian River tributaries in the lower basin.

"The detection levels so far have not been alarming, but we want to do everything we can to minimize the spread," said Morgan Kilgour, North Central regional manager for the California Department of Fish and Wildlife.

Dry Creek, which flows by Warm Springs Hatchery, was previously identified as positive for the snails. The source of the recent detections is not known but it is suspected the snails came to the hatchery from its source water of Lake Sonoma, state officials said Friday.

For the time being, the hatchery will continue to operate its Coho and steelhead programs.

In addition to continual surveys, CDFW has increased biosecurity measures at the hatchery and is working with the U.S. Army Corps of Engineers and the National Oceanic and Atmospheric Administration to determine if the detection calls for any changes in Coho release protocols.

High-density populations of the tiny snail are likely to cause substantial negative impacts on fisheries by replacing preferred, nutritious foods. A study showed that trout with the invasive species in its guts had significantly poorer body conditions than those without. In feeding trials, rainbow trout that were fed an exclusive diet of unlimited invasive New Zealand mudsnails showed that 54 percent of the mudsnails were still alive through the digestive tract and the trout subsequently lost up to 0.48 percent of their initial body weight each day, which is nearly equal to the impact of starvation, according to the California Department of Fish and Wildlife.

The invasive species was first discovered in California in 2000 in the Owens River. Officials believe the snails entered western rivers through shipments of live sportfish, although the subsequent spread has likely been due to recreational activities.

Mudsnails easily attach to boots, waders, clothing, shoelaces, watercraft, aquatic vegetation and gear, and can easily go unnoticed due to their very small size. As a result, they are commonly transported by unsuspecting anglers, boaters, other water recreationists, or even wildlife, including harvested fish. Mudsnails also disperse through floating freely or on algal mats, or by surviving passage through fish guts.

To keep the invasive species from spreading farther, people fishing or boating in the Russian River and any of its tributaries are asked to decontaminate any equipment used in the river by following the "Clean, Drain and Dry" method:

• If you wade, freeze waders and other gear overnight (or for at least six hours).
• After leaving the water, inspect waders, boots, float tubes, boats and trailers or any gear used in the water.
• Remove any visible snails with a stiff brush and follow with rinsing. If possible, freeze or completely dry out any wet gear.
• Never transport live fish or other aquatic plants or animals from one body of water to another.