Exotic invaders threaten famous
Silver Creek being overrun
by New Zealand mud snails
By GREG STAHL
Express Staff Writer
The world-famous fly fishing
waters of Silver Creek are being invaded by a minuscule creature that
could have a big impact.
New Zealand mud snails are
small, but thick in many rivers throughout Idaho and the West.
The New Zealand mud snail is one
of dozens of plant and animal species that are threatening agriculture,
industry, wildlife and recreation throughout Idaho, and, like other
invasive species, it is spreading unchecked through the waterways of
Idaho and North America.
Gov. Dirk Kempthorne announced
Tuesday, Feb. 17, at a conference on invasive species in Boise that the
Idaho Department of Fish and Game will team up with The Nature
Conservancy-Idaho to seek ways to prevent the snail from devastating
Silver Creek, near Picabo, and other Idaho streams.
"Silver Creek will become an
outdoor laboratory on how to limit the spread of these species,"
As its name indicates, the New
Zealand mud snail is native to the freshwater lakes and streams of New
Zealand. A single snail is tiny, measuring several millimeters across,
but they populate streams in extremely high densities.
The snails were first detected in
the U.S. in the mid-1980s in the mid-Snake River near Hagerman. Since
then, they have mushroomed to the waters of Montana, Wyoming,
California, Arizona, Oregon and Utah. They have infiltrated the Firehole
River and other popular fishing streams in Yellowstone National Park.
The spread of the snails is
caused, at least in part, by anglers or boaters who pack muddy waders or
equipment from river to river.
For that reason, cleaning stations
will be established along Silver Creek to slow or stop further spreading
of mud snail populations.
The serenity of Silver Creek
belies the turmoil under the water, where an invasive species, New
Zealand mud snails, is waging a war against the streamís natural
ecosystem. Express photo by Ken Retallic
According to TNC, the
extraordinary density of snails that has been discovered in some Western
streams is a cause for serious concern. In some cases, biologists have
counted more than 500,000 snails in a square meter of river. They can
out-compete aquatic invertebrates like mayflies and caddis flies and
have a relatively low nutritional value as a food source for fish, said
TNC communications director Matt Miller.
In extreme cases, mud snails
comprise up to 95 percent of the invertebrates in a river.
Mud snails were one of the
featured species discussed at TNCís Silver Creek Symposium held in
November at Sun Valley. Because mud snails are relatively recent
invaders, little is known about their long-term impacts on waterways.
Also, because they reproduce asexually, even one survivor is enough to
repopulate a stream, Miller said.
Invasive species, defined as any
species non-native to a region that harms economic, environmental or
human health, cost Americans an estimated $137 billion each year.