Invasive water fleas found in Wisconsin lake

Oct. 7, 2003

Photo of water flea

This is a microscopic view of Bythotrephes cederstroemi, aka the spiny water flea. This invasive species has been found in a lake in Iron County near Lake Superior. (Photo: Pieter Johnson)

Just weeks after the state's first snakehead fish turned up in the Rock River, another invasive species has been found in Wisconsin waters.

UW-Madison and the Wisconsin Department of Natural Resources (DNR) report Oct. 7 that spiny water fleas (Bythotrephes cederstroemi) have invaded the Gile Flowage, a lake in Iron County near Lake Superior. This is the first time the invasive water fleas have been found in an inland Wisconsin lake, according to the DNR.

Spiny water fleas - a type of crustacean measuring up to one-half inch long - had invaded Lake Huron by 1984 and spread to every Great Lake by 1987. To date, they have moved to inland lakes in Michigan, Minnesota and southern Ontario in Canada.

Scientists suspect that the critter - whose spiny, sharp tail makes up half its body length - first arrived in North America in water carried aboard freighters from European ports.

The discovery of the spiny crustacean in the Wisconsin lake surprised Pieter Johnson, a UW-Madison zoology graduate student whose research sampling revealed the exotic creatures.

"Most of the lakes where the water fleas are found are deeper, clearer, colder lakes," explains Johnson, adding that the Gile Flowage, with a maximum depth of 25 feet and a surface area of 3,300 acres, doesn't fit the profile. His concern is that if the crustaceans are invading shallower lakes, then they also may be invading other ones.

Like many invasive species, spiny water fleas threaten the abundance of native species by diminishing their food sources. For instance, the water fleas compete with small and juvenile fish for zooplankton. But, because it can reproduce more quickly, this invasive species can gobble up the food source, leaving few leftovers for smaller fish. Many fish, except the larger ones, can't eat the water fleas due to the critters' barbed spines.

"The water fleas decrease the diversity and abundance of zooplankton available to small fish," says Johnson. "How this might cascade up or down the food chain remains speculation. It has the potential to hurt fisheries and reduce the number of game fish."

Follow-up sampling on the Gile Flowage, Johnson adds, has shown that the spiny water fleas are abundant and reproducing in all parts of the lake. These factors, he says, may increase the ease with which the invasive species is transferred to other lakes.

Ron Martin, DNR water resources management specialist, says that the presence of spiny water fleas in the Gile Flowage will make it easier for them to spread to other inland lakes. "We're very concerned about spread to other lakes in Iron County and surrounding counties - especially Vilas - because it has more lakes than any Wisconsin county," explains Martin. "It's possible for the fleas to reach a density where they cause problems not only for anglers, but also for the overall ecology of the lake."

No effective strategy is available to control the spiny water fleas once they are introduced to lakes, Martin adds.

To stop the spread of spiny water fleas to other inland lakes, Johnson has been working with the DNR to create awareness and educate the public about the active role they can play in protecting Wisconsin lakes from this invader.

For example, the DNR has established guidelines for preventing the spread of invasive aquatic species, including spiny water fleas, and have posted these guidelines on signs at all the Gile Flowage boat landings, says Martin.

Martin recommends boaters and anglers take the following steps to prevent the spread of spiny water fleas to other inland lakes:

* Learn what Wisconsin's aquatic invasive species look like, including spiny water fleas.

* Inspect boats, trailers, boating equipment (e.g., anchors, rollers and axles) and fishing equipment (e.g. rods and lines), and remove any plants, animals or mud before leaving the water. All these materials, including rod eyelets, can carry spiny water flea eggs.

* Drain all water from motors, livewells, bilge and transom wells, and empty bait buckets on land while still at the boat landing. Anglers should never release live bait into a water body or release aquatic animals from one water body into another.

* Wash boats, trailers and other equipment with hot and/or high pressure water to kill harmful species that weren't visible at the boat landing, or let boats and equipment dry completely for five days.

"We want to be as proactive as possible in preventing the spread of these creatures into other Wisconsin lakes," says Martin, "and we need the help of all boaters and anglers to do so."

Martin urges anyone who thinks they've spotted spiny water fleas in other inland Wisconsin lakes to contact their local DNR office or call (608) 266-9270.

Johnson adds, "If we can get the word to boaters and anglers about what they can do to help, I'm optimistic we can slow down or even stop the spread of this invader."