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Great Lakes Article:

Exotic water flea hops to inland waters, threatening fish
By Susanne Quick
Milwaukee Journal Sentinel
10/07/03

Wisconsin's inland lakes are on the verge of being infested by fleas. Not the kind that you find on dogs and cats, but a European crustacean called the spiny water flea.

A University of Wisconsin-Madison graduate student found the barbed bandits in Gile Flowage, a large lake in Iron County near Lake Superior.

"We had a hunch they'd be there," said Pieter Johnson, the UW graduate student in limnology, referring to the presence of fleas on inland lakes in Wisconsin.

Although the exotic water fleas have been living in the Great Lakes for more than 15 years, this marks their first appearance in the state's inland waters.

The fleas are a concern because they compete with and eat native zooplankton - the food of young sport fish, like walleye and perch, and small foraging fish, like minnows.

"The water fleas decrease the diversity and abundance of zooplankton available to fish," Johnson said.

How this might affect the food chain remains speculative, he said. But "it has the potential to hurt fisheries and reduce the number of game fish."

The spiny water flea looks something like an alien/helicopter hybrid. With big black eyes, a bulbous sac sitting above its head, and a long, barbed, whip-like tail, the flea swims around attacking zooplankton and other aquatic delicacies.

According to Philip Moy, a non-indigenous fisheries specialist with UW-Manitowoc and the Wisconsin Sea Grant Institute, the spiny water fleas have been known to eat very young and tiny fish, too.

The flea, which measures about a half-inch long, has four sets of legs. The first two legs are extra-long and enable the flea to catch its prey. The other three sets are used to restrain the victim while it is consumed.

But it isn't their killing style that has resource managers concerned; it's their appetite for daphnia - a type of zooplankton - and their superior sexual skills. During the summer, a water flea can produce as many as 10 offspring every week.

And according to Moy, the combination of prolific reproduction, a hearty appetite and a tail like a medieval mace makes this tiny crustacean a formidable foe.

Not only are they voracious consumers of large species of daphnia, but they also are inedible to fish that would normally eat the native zooplankton.

"Even if a little fish could swallow them," Moy said, they'd end up with a belly full of tough, sharp spines - a sure way to puncture and tear the intestinal tract of a small fish.

The Minnesota Department of Natural Resources reported its first inland flea intruders last week. Michigan and Ontario have had them for a couple of years.

The scary thing is that once they are found it doesn't take long for a whole region to be infested, said Jake Vander Zanden, a UW-Madison professor of limnology, who worked with Johnson on the water flea project.

The water fleas are adept at hitchhiking from lake to lake in bait buckets, boats' live wells and bilges.

And although the fleas don't last long out of the water, the proximity of Gile Flowage to the lakes of Wisconsin's northern highlands has Vander Zanden concerned.

"It's in striking distance" of the lakes to its south, said Vander Zanden, who believes it's just a matter of time before the fleas settle into Wisconsin's lake district.

The other concern is that although individual fleas don't fare well out of the water, they are capable of producing something called a "resting egg" - a resilient egg sac that can encase and keep alive a few young fleas for years on end.

This could mean that even if someone kept a boat out of the water for a couple of days - drying out and killing any vagabonds - the resting eggs could survive. And it'd just take re-immersion to wake up these dormant fleas.

In any case, said Vander Zanden, "once they've been established in a lake," the fleas are pretty much there to stay.

Indeed, they are already considered permanent members of the Great Lakes, said Moy, the UW-Manitowoc fisheries expert. But figuring out what kind of damage they have caused on that ecosystem is hard to determine "what with zebra mussels and everything else" already wreaking havoc.

Prevention is the key to halting the threat of spiny water fleas, said Steve AveLallemant, Wisconsin DNR water resources management specialist.

So signs and a determined effort to inform boaters and anglers about the water fleas is already under way, AveLallemant said.

And Johnson is hopeful that with a determined communal effort, the fleas can be contained.

"We're lucky," he said, "we caught them early on in the invasion - they are in just one (inland) lake."

AveLallemant agreed that introduction of the fleas from the Great Lakes is not likely. But it's the fact that they are inland - with people using the same boats to move between inland lakes - that has him worried.

"There is increased potential for expansion," he said. "I guess we're at a kind of wait and see."

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