Spiny water fleas.
They sound innocent enough. But don't let the name fool you. They're an invasive species, and they were recently discovered in Lake Mille Lacs.
The DNR announced Tuesday that the Aitkin Area Fisheries staff found spiny water fleas in Mille Lacs last week. The discovery of the invasive species is the first outside of Lake Superior and the U.S.-Canadian border waters, such as Lake of the Woods, Rainy Lake and Namakan Lake.
Rich Rezanka, DNR invasive species specialist in Region 2, which runs from Brainerd to the Canadian border, said spiny water fleas are zooplankton and a distant relative of crabs, crawfish and shrimp. They have a long tail spine with up to three pairs of barbs, which makes them difficult for smaller fish to eat. As a predator, they feed on zooplankton, competing with smaller fish for the food, and they often become abundant in late summer and fall.
The spiny water flea has a long tail spine and is 1/4- to 5/8-inch long. DNR
"They (spiny water fleas) aren't uncommon, but they have a competitive advantage in that they have a huge, long tail on them with spikes," Rezanka said. "It's thought that small fish, especially fry, have trouble eating these things. They compete with these fish by eating the food (the smaller fish) normally eat but they can't be eaten themselves."
Although it has experienced several down years recently, Mille Lacs is still regarded as one of the top walleye fisheries in the state. Will that change with the discovery? Probably not. But the find shouldn't be taken lightly.
"It could be an issue with the perch population, but they're (DNR's Aitkin Area Fisheries staff) not really as concerned with the walleye population because walleyes have the ability to open their mouth wider and can eat these things," Rezanka said. "But if it screws up the perch population it could screw up the walleyes, too.
"So is it a big deal? Yes it is. In the Great Lakes, they found that it made some changes in the food web. But is it the end of Mille Lacs as we know it? No. We're very concerned about it and don't want it to get (transferred) out of Mille Lacs. We're disappointed it's there. But it's not the end of the world."
The water fleas can collect in masses, sticking to fishing lines, downrigger cables and anchor lines. The masses can resemble gelatin or cotton batting with tiny black spots, which are the creatures' eyes or eggs. Individual organisms are difficult to distinguish without magnification because they are only 1/4- to 5/8-inch long. Anglers are often the first to discover the water fleas because they become tangled to fishing gear. The water fleas can be a nuisance, collecting in gobs on fishing lines.
"It's a big concern," said Rick Bruesewitz, Aitkin Area Fisheries supervisor. "We had a clump (of spiny water fleas) on one of the staff's fishing lines or downrigger cables. That's how we first became aware of it. And when they looked at the samples in St. Paul they observed those in the samples. It could affect boats, water, fishing equipment."
And, this time of year, much more.
"We're not taking it lightly and we want people to take it seriously, especially this time of year. There's a new group of people using the lake with duck hunters," Rezanka said. "They're putting out decoys, and in pulling in their lines and going to another lake they could easily transport them from lake to lake."
The find comes on the heels of the discovery of zebra mussels in the lake. As a result, regulations prohibiting the transport of water and requiring the draining of livewells, bait containers and bilges are already in effect at the lake.
In response to the new infestation, the DNR said it also will update the signs at water accesses on Mille Las to indicate the presence of the water fleas, continue watercraft inspections and enforcement efforts around the lake that were increased this year due to zebra mussels, provide area businesses with information on spiny water fleas and monitor spiny water flea populations as part of an assessment of impacts to the lake.
Before leaving the water access, the DNR urges boaters and anglers to remove aquatic plants and animals, including gelatinous or cotton-batting-like material from fishing lines, downrigger cables, anchor ropes or waterfowl decoy cords and drain water from livewells, bait containers and bilges by removing the drain plugs. Those who want to keep live bait must replace lake or river water with tap or spring water. Boaters and anglers also should dispose of unwanted live bait in the trash, spray watercraft and gear with hot high-pressure or hot tap water for several minutes before transporting to another water or dry the watercraft and gear thoroughly for at least 24 hours and preferably five days before transporting to another waterway.
"The water flea adults live for maybe a day out of water but the eggs they produce this time of year live long, maybe a couple of days," Rezanka said.
Experts believe spiny water fleas originally arrived in the U.S. from Eurasia in the ballast water of cargo ships. They were first found in Lake Superior in 1987.
"I can't give you a prediction of what will happen 50 years from now or five years from now, but it's never a good thing to have these things around," Rezanka said.
"Instead of a three-hour run from the Great Lakes, now we've got this spot in the middle of Minnesota that's got these things."
BRIAN S. PETERSON may be reached at firstname.lastname@example.org or 855-5864.
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