Foreign snail invading California waters
January 29, 2004
They are quite small at about one-eighth of an inch, but they can take over drainage in pretty short order. This small brown snail feeds on algae and has no natural predators. As a result, there is little or no food for the other aquatic insects and native snails.
Since they provide little nutritional value to fish, fish populations will suffer. The end result is a fishery in risk of collapse. There is no known way to eradicate them once they are present. In New Zealand, they are controlled by a tiny parasite, which gives us some hope of a possible biological measure.
Originally found in New Zealand, the NZMS was transported to England in 1859. By 1899, it had reached mainland Europe and by the 1920s it was found throughout England. In 1987, NZMS were discovered in Idaho’s Snake River. In 1997, surveys showed the snail had spread to all of the major waters in Yellowstone National Park.
In recent years it has been found throughout the Columbia River drainage, including many Montana waters and several California streams. Because they are so small, biologists feel that they may be in more waters than currently identified.
The discovery of the NZMS in October 2003 at Putah Creek, below Lake Berryessa, has the Department of Fish and Game (DFG) extremely concerned. They have temporarily closed the creek for 120 days to fishing. The closure will be temporary while affected agencies determine the extent of the infestation and the appropriate course of action. Closing the creek to angling will help prevent the unintentional spread of NZMS from Putah Creek to other waters.
Another recent find in December 2003 in the Mokelumme River has elevated awareness of the potential problem. The NZMS was originally found in California in the Upper Owens River, from Crowley Reservoir, upstream about five miles, sometime in 2000. It was also found in Hot Creek and the Bishop Creek Canal.
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Because these snails can survive up to 25 days if they are in a moist environment, anglers are one of the primary concerns of transporting these snails to other waters. They can also close off their shell opening allowing them to live for significant lengths of time without being in the water. They can be transported on or in waders, muddy wader boots, in live wells or in cooling systems at cool temperatures.
It only takes one snail to begin populating a lake or stream. The California DFG suggests that anglers treat their gear with at least one of the following methods to prevent spread of the NZMS:
— Spray gear with Clorox Formula 409, and then scrub with stiff-bristled brush to remove all visible snails. Follow the procedure with a careful inspection of waders and gear to insure the removal of all adults. Finish with a tap water rinse. Snails frequently collect between laces and the tongue of wading boots and in the boot’s felt soles.
— Freeze waders six to eight hours. It is best to leave them in the freezer overnight to ensure complete mortality.
— Drying in air over 112 degrees for 24 hours will eliminate all mud snails. Alternatively, place gear in water maintained at 130 degrees for five minutes. Mortality of snails varies by exposure to heat and humidity at different combinations.
NZMS are not the only aquatic invasive species spread by anglers and boaters. Live bait and the packaging used for some forms of live bait are known to spread other invaders. In addition, invasive aquatic plants and animals are known to hitchhike on boats, their propellers, live wells, and fishing gear. Cleaning all boating equipment is crucial to reducing the impacts from non-native invasive species.
While the DFG suggests the above as effective, others suggest that Formula 409 is ineffective and regular Clorox brand bleach is the best to use. Two tablespoons per quart of water is the recommended dosage. This treatment is said to kill snails in five minutes.
There is a terrific article by Ralph Cutter in the February 2004 edition of California Flyfisher magazine. Cutter suggests using a biodegradable alternative in grapefruit seed extract, marketed in health food stores as GSE. However, this option needs water temperature above 45 degrees to be effective.
The DFG warns that the snails in Putah Creek have been collected on the banks, well away from the water’s edge. Outdoor enthusiasts and boaters who travel within the riparian areas should also follow the above guidelines.
Also, be careful when cleaning fish and disposing of the innards. Dispose of them properly. Don’t toss them into the water. While Anglers are certainly not the only source of the spread of these creatures, they are one of the most obvious.
Please take great care with your equipment when fishing in any water since the NZMS could be present, but undetected. Clean and store your gear properly to prevent the spread of this very serious threat to our local fishery, and spread the word to other anglers and recreational enthusiasts.
Bruce Ajari is a Truckee resident. “Gone Fishin'” appears weekly in the Sierra Sun during the regular fishing season.