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Mudsnails, aquatic weeds invade Eleven Mile

Fairplay Flume 08/20/11
Mudsnails, aquatic weeds invade Eleven Mile
Possible effects include smaller fish and dense weed mats

Quintn Parker and Tom Locke
Correspondent and Editor

Wildlife monitoring crews have recently confirmed that two invasive species - New Zealand mudsnails and an aquatic invasive weed, Eurasian watermilfoil - have been found at Eleven Mile Reservoir, according to an Aug. 12 press release from Colorado Parks and Wildlife.

The New Zealand mudsnail cannot be controlled, reproduces very rapidly and could lead to smaller fish in Eleven Mile, while the Eurasian milfoil can be controlled but not eradicated, and it could lead to dense weed mats in the reservoir that could make it difficult to navigate for swimmers or boaters, Elizabeth Brown, invasive species coordinator for Colorado Parks and Wildlife, told The Flume.

"Eleven Mile State Park is a fabulous place, and it will continue to be so. It's something we're going to have to manage," said Brown. "We're working on a strategy."

Eleven Mile State Park is of significant importance to Park County. In 2009, it drew 309,266 visitors, and between June 2008 and May 2009, $15.7 million was spent by non-resident visitors to Eleven Mile, according to survey results released Sept. 2, 2010. (See the Oct. 1, 2010, Flume.)

New Zealand mudsnails

With respect to the New Zealand mudsnail, "there are no control methods that we could use at Eleven Mile Reservoir, so really the goal is to prevent it from moving [to other bodies of water]," said Brown.

The introduction of the New Zealand mudsnail into Eleven Mile Reservoir, which is in southeastern Park County, could possibly lead to smaller fish in the reservoir, said Brown. The mudsnail outcompetes native mollusks and invertebrates that are the base of the food chain for fish. But a fish can't digest the New Zealand mudsnail, so it provides no nutrition for the fish when it is eaten. Thus the fish might be smaller because of less nutrition.

The New Zealand mudsnail hasn't been in Colorado long enough to predict the possible effects, or the timing of the effects, on Eleven Mile, according to Brown.

The New Zealand mudsnail is native to New Zealand and was first discovered in the United States in the late 1980s in Idaho. It was first discovered in Colorado in 2004, when it was found both in Boulder Creek and in the South Platte River below the Eleven Mile Reservoir dam, Brown said.

It's not clear how the mudsnail got into Eleven Mile Reservoir. It could have been brought by a fish, because fish eat them but can't digest them, so they eventually come out of fish undigested. Or it could have been brought by waders of a fisherman, Brown said.

The New Zealand mudsnail is very small, about the size of a poppyseed, generally growing to about an eighth of an inch. Nevertheless, the New Zealand mudsnail is very troublesome due to its easily massive numbers and impressive resilience. A single snail can live for 24 hours without water. On a damp surface, however, it can survive for up to 50 days.

Mud-snails reproduce parthenogenetically, which essentially means by cloning themselves. It only takes a single snail to produce an invasion.

According to Gary Busteed of the National Park Service, a single snail can result in a colony of more than 40 million snails in less than one year.

Kevin Tobey the park manager for Eleven Mile State Park, could not be reached immediately for comment.

Eurasian milfoil

For the Eurasian milfoil, the invasive weed that produced a final positive test on Aug. 7 as being present at Eleven Mile, there are "different ways to control it," and Parks and Wildlife is "exploring options," said Brown. "You're not going to eradicate it or get rid of it."

It can "form a dense weed mat that can make it difficult to navigate through, whether you're swimming or boating," said Brown.

She said she couldn't predict how fast the Eurasian milfoil might spread at Eleven Mile.

It is scattered throughout the Front Range, is in quite a few Colorado reservoirs, and first entered the U.S. from Eurasia and northern Africa. It was first recorded in Colorado in 1999, Brown said. She said it could have an impact on water supply systems.

It out-competes other plant life and could have an impact on cover and food for fish, according to Parks and Wildlife spokesman Randy Hampton.

The main message is that every fisherman can make a difference in helping to avoid the spread of invasive species, Brown said. They should be very careful to clean their waders to make sure no mud or plants are on them that might be taken to another body of water.

Invasive species

Both the New Zealand mudsnail and the Eurasian watermilfoil are invasive species, but what exactly is that?

An invasive species is any type of flora or fauna that invades an ecosystem and throws the environment out of balance. A well-known example of this is the cane toad, which was brought across the ocean from South America to Australia. Once in Australia, the cane toads spread rapidly due to no natural predators and proceeded to consume massive amounts of resources, greatly damaging the ecosystem.

Rusty crayfish (Orconectesrusticus), first discovered in 2009 in the headwaters of the Yampa River, have been recently confirmed in the reservoir at Stagecoach State Park, near Steamboat Springs. The rusty crayfish is an invasive species native to the Ohio River. It has had negative ecological effects on aquatic ecosystems in at least 16 other states and in parts of southern Canada.

"Rusty crayfish are a tenacious invasive species that have the potential to impact streams and lakes," said Greg Gerlich, the Colorado Division of Wildlife's aquatic section manager.

The fresh-water crustacean, known for being extremely aggressive, will out-compete native species for food and habitat. Rusty crayfish will even displace native crayfish and weaker species from secure areas, making them more vulnerable to predators and potential extinction. They will often clear large areas of aquatic plants, reducing overall habitats.

In order to prevent the further expansion of the rusty crayfish, Colorado law prohibits the use of rusty crayfish as bait anywhere in the state. However, identification of rusty crayfish is very difficult and often requires laboratory analysis. Due to the identification challenge, it is unlikely that most anglers will be able to identify rusty crayfish from other crayfish found in a reservoir.

"The fact that we're finding new populations means we have to work harder to engage the public to do their part to clean and dry all their gear and equipment as well as their boats to protect our waters," said Brown in the Aug. 12 press release.

In an effort to educate about invasive species, both Colorado State Parks and the Colorado Division of Wildlife started campaigns following the initial discovery of New Zealand mudsnails in Colorado.

Earlier this year Gov. John Hickenlooper signed legislation that merged the separate programs of Colorado State Parks and the Colorado Division of Wildlife, partly in order to more efficiently provide education and solutions surrounding the invasive species problems. Now they are combined into a single division Colorado Parks and Wildlife, under the Colorado Department of Natural Resources.

"We committed on our first day in office to making government more efficient, effective and elegant," said Hickenlooper in the Aug. 12 press release.

It says the most important thing anglers can do is to remove all mud, plants and organic material from their waders and equipment after every use. For maximum effectiveness, anglers should submerge waders and gear in a large tub filled with a mixture of half Kitchen Formula 409 and half water for at least 10 minutes. If such items are not available, water greater than 140 degrees Fahrenheit should suffice. [truncated for length]
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