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Tahoe invaders: Non-native species threaten lake

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Tahoe invaders: Non-native species threaten lake

Postby SteveB » Sat May 05, 2007 12:38 pm

From the Saturday 05/05 issue of Reno Gazette-Journal:
Posted: 5/5/2007

An aggressive program to protect Lake Tahoe from aquatic invaders is being launched, with experts agreeing there's little time to lose.

During a two-day conference last week at the lake, scientists and land-use managers said efforts to protect Tahoe from invasive species must be stepped up immediately.

"People are freaking out. And we should," said Sudeep Chandra, a University of Nevada, Reno researcher who participated in the meeting at the Tahoe Center for Environmental Science.

The sense of urgency stems primarily from the threat posed by the quagga mussel, an invasive mollusk that has overrun the Great Lakes region and was discovered thriving in Southern Nevada's Lake Mead four months ago. Experts fear the mussel could be easily transported to Tahoe's cobalt waters as stowaways on pleasure boats, causing widespread environmental and economic problems if they become established.

Other invaders are already in the lake. Eurasian watermilfoil, an aggressive underwater weed, has spread across much of Tahoe since scientists began tracking the problem in 1994. Another invasive weed, curlyleaf pondweed, was discovered four years ago and is being carried east across Tahoe's waters by prevailing winds and currents.

Non-native warm-water fish, including bass, crappie, bluegill and gold fish, are also beginning to flourish -- possibly aided by warming waters associated with climate change, scientists said.

Taken together, invasive species already present or threatening to arrive pose a major threat to the alpine lake.

"The news is not good," said Lars Anderson, a U.S. Department of Agriculture scientist who has tracked the movement of invasive weeds through Tahoe's waters. "How do we know we've got a problem? We're seeing it spread."

To a large degree, Tahoe's ecosystem has already been profoundly altered by non-native species, many often deliberately introduced by humans.

Lahontan cutthroat trout, nature's top-of-the-line predator at Lake Tahoe, vanished from the lake in 1939. Overfishing and habitat destruction were partly responsible for the cutthroat's departure, but so was the introduction of the aggressive, non-native Mackinaw trout in the early 1900s as a game fish. Other game fish in the lake -- rainbow trout and kokanee salmon among them -- were also planted by people, not nature.

Crayfish were planted in the lake; and today, as many as 45 million thrive in its waters. They could provide a major food source for the bass that officials don't want to see in Tahoe. Watermilfoil also offers good bass habitat.

Planting non-native species often comes with unintended consequences, and Tahoe offers no exception. In the early 1960s, mysis shrimp were introduced to Tahoe with the idea they would provide a new food source for kokanee salmon to make the game fish bigger for anglers.

The shrimp preyed on the lake's zooplankton, causing a dramatic drop in plankton populations and a significant shift in the lake's ecosystem.

"It's restructuring the whole food web," Chandra said of the shrimp's impacts.

Boats pose danger

Modern invasive threats have much to do with boating. Eurasian watermilfoil was probably introduced to the lake as fragments attached to pleasure boats. Boats have likely helped spread the weed around the lake to many marinas as well as Emerald Bay, Tahoe's most popular boating destination.

The weed grows thick in South Lake Tahoe's Tahoe Keys, where homeowners pay more than $200,000 per year to cut milfoil so boating channels can stay open.

"We're doing everything we can, but it's pretty much a losing battle," said Ed Morrow of the Tahoe Keys Homeowners Association.

The same boats spreading milfoil around the lake could also bring the quagga mussel. Experts attending last week's conference agreed an aggressive program to inspect and wash boats before they enter the lake should be enacted before this summer's boating season is in full swing.

A boating survey conducted at Tahoe last summer and in 2005 showed 18 percent of boaters surveyed did nothing to clean their boats, while 51 percent did little but wipe their vessel down. Some cited Tahoe's pure waters as the reason they don't bother to clean their vessel, said Marion Wittmann, a researcher for UC Santa Barbara who conducted the survey.

That poses a very real threat should any boats entering Tahoe come with quagga mussels attached, experts agreed.

"The quagga is going to get here the same way the plants got here," Anderson said.

"You have the pathway here," agreed Jeff Herod, a mussel expert for the U.S. Fish and Wildlife Service who investigated the quagga invasion at Lake Mead.

Lake Tahoe's waters are low in calcium, a substance needed for the mussels to grow their shells. Some experts believe that fact should help protect the lake. Herod isn't so sure; he suspects localized areas with higher calcium levels could exist and provide a "foothold for invasion."

"I don't have confidence that Tahoe is not at risk," Herod said.

Effort takes shape

Last week's conference in Incline Village represented an important step in recognizing the threat posed by aquatic invasive species, but much more proactive action is needed, participants agreed.

Ongoing efforts to control watermilfoil with scuba divers removing the weed by hand should be expanded around the lake, experts said. And, they said, serious attention should be paid to the possibility of using herbicides to kill the weed at the Tahoe Keys, the most infested place on the lake. That idea has so far run into resistance from California water quality officials.

John Singlaub, executive director of the Tahoe Regional Planning Agency, said the battle against invasive plants and animals should be made a top priority. Singlaub said he plans to discuss funding the program, including the hiring of an individual to head it up, with officials from Nevada's State Lands Division and California's Water Quality Control Board. Some decisions are expected within a month.

Other important steps -- including boat-washing regulations -- are included in the agency's yet-to-be-approved "blue boating program."

Singlaub said it's not enough to control invasive species at Lake Tahoe. If possible, Singlaub said, they should be eradicated from the lake, which Congress has targeted for special protection.

"We should set the bar high for ourselves right now," Singlaub said. "If we can't do it here, where can we do it?"

Sidebar notes:

Tahoe invasives
Aquatic invasive species present at Lake Tahoe

Eurasian watermilfoil: Native to Eurasia, the aquatic plant has invaded much of the United States and Canada. Milfoil probably arrived at Lake Tahoe sometime in the 1970s, introduced as plant fragments carried by pleasure boats. It currently infests about 10,000 acres all around the lake, including Emerald Bay and many marinas. It has escaped into the Truckee River. Milfoil crowds out native vegetation, uses oxygen needed by fish and contributes to algae growth.

Curlyleaf pondweed: First found in Lake Tahoe in 2003, this plant native to Eurasia has spread to several locations along the lake's south shore and is spreading east follow prevailing winds and currents. The plant forms in dense mats that can interfere with fish movement and boating.

Largemouth and smallmouth bass, bluegills, crappie and gold fish. Several types of non-native, warm water fish exist in Lake Tahoe. Most appear to have been introduced to the ecosystem near the Tahoe Keys. These fish can be extremely detrimental to the lake's natural food web.

The American bullfrog: The non-native amphibian is found in drainages along Tahoe's south and east shores. Extremely prolific and aggressive predators, bullfrogs can displace other amphibians or reptiles and threaten biodiversity.

Potential invasive threats

Quagga and zebra mussels. Non-native, freshwater mollusks have invaded much of the country. Quagga mussels were discovered this year to be thriving in southern Nevada's Lake Mead and Lake Mohave and California's Lake Havasu. It is feared boaters could bring the mussels to Lake Tahoe, where they could overrun the ecosystem, damage native species, clog water intakes and damage boat engines.

New Zealand Mud snails: The non-native invertebrate is found throughout much of the West, including the Snake River system and in California's Owens Valley. The snail reproduces rapidly and can displace native invertebrates.

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Postby SSSdave » Sun May 06, 2007 9:37 am

Lake Tahoe and its Truckee River are monuments to ecological destruction due to humans. Can't really roll back the clock now. The invasive species situation is of course regularly getting worse even though it pains the mind to imagine our disasterous influences are finding new ways to destroy the little natural that remains. Ever since the basin was given over to mindless real estate and commercial interests like the gambling industry, the fate of the lake has pretty much been hopeless. Of course the greedy inconsiderate, selfish miners, loggers, and commercial fishermen of a century ago didn't leave much natural after they exploited the basin and then spent much of their money on whiskey and whores in Virginia City.

What ought to be done to Lake Tahoe? Well the government slowly over time ought to buy up Tahoe Keys residence by residence by taxing the Casino industry. After all South Lake Tahoe is a cesspool largely created by that industry. Owners would not be able to sell to anyone but the government. They would have the lifetime of the current owners to do so. As the government bought up those places they would convert those lands back to the natural state they ought to be for the better health of the lake. If they don't, that key area where the Upper Truckee River enters the lake will always be the source of the worst polution and entry point of alien invasive species. It is simply uncontrollable as is. One can pretty much predict some drunk moron is eventually going to toss in northern pike after visiting lakes in eastern Nevada that already are infested with such vermin. Tahoe Keys was condemned decades ago when created though government at the time was too weak to stand up to the big bucks of those days. Of course we can expect all manner of alien fish or aquatic weeds to occassionally appear in the lake because as long as there are hundreds of residences with boat slips right in their backyard, one can guarantee a few scum will always care little about what the majority wish. ...David :nod:
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