Invasive zebra mussels are working their way west from the Great Lakes to the Rainy-Namakan basin while other invasive species already in the water system continue to spread. Local officials are trying to slow and halt their progress through a combination of education, outreach and boat inspections.
Derrick Passe, Rainy River coordinator with the Lake County Soil & Water Conservation District, said species like zebra mussels, spiny waterflea and rusty crayfish can wreak havoc in ecosystems around Rainy and Namakan lakes, devouring food and pushing out competitors while making it harder for larger predatory fish to catch their own meals. These sneaky creatures can hitch a ride on boats and watercraft and reach new lakes and rivers over land – precisely how the spiny waterflea made it from Lake Superior into the Rainy basin, Passe explained.
Zebra mussels start out as microscopic eggs and larvae that can survive up to a week in the water in or even in damp spots on a boat, and the only reliable way to kill them is with hot water heated over 180 degrees Fahrenheit (82 C) for about two minutes. Spiny waterflea may not be microscopic, but their small size and ability to enter a “resting state” that lets them survive in mud or even pure bleach leaves drying them out as the main method of stopping their expansion. Rusty crayfish, which made their way into the region originally as bait, continue to be spread by anglers and possibly through science classes releasing animals after their experiments are completed.
Both Minnesota and Ontario have made efforts to limit the spread of these and other species. Passe said the state and province are encouraging people to make sure their boats, canoes and wading gear go through the clean, drain and dry process: cleaning off all the mud, draining all the water out and then letting it dry, ideally at least overnight. Going through this process before entering another body of water can help keep unwanted creatures out.
In Minnesota, Passe said the state also has boat inspections that typically take place at the ramps to the lakes. The Ontario Invasive Species Act, which came into force last November, also gives Ontario Ministry of Natural Resources and Forestry officials the authority to inspect any vehicle, including boats, if they suspect they could contain invasive species. Christopher Martin, management biologist with the Kenora district of the Ministry, said his district does not currently conduct inspections or operate boat cleaning stations, though he added that authorities in Thunder Bay are starting their own boat cleaning programs there.
The impacts these diminutive creatures can have on the ecosystem is massive. Zebra mussels are filter feeders that suck up large amounts of algae and other microscopic food, keeping it out of the mouths of native species and disrupting the food chain, ultimately creating impacts all the way to popular sportfish. Spiny waterflea feed on daphnia, a tiny crustacean already eaten by preyfish, and feature a huge spine that can poke holes in perch stomachs if those fish are smaller than five centimeters. It’s also not as nutritious as native organisms are for those perch, which can lead to health problems for the fish if their diet is too heavy in spiny waterflea.
“You’re feeding fish popcorn instead of vegetables,” Passe said.
Rusty crayfish not only out-compete the native crayfish, but grow too large for fish like bass to devour and thus become an ongoing nuisance. Passe referred to them as a “little lawnmower” that cuts down aquatic vegetation, including wild rice. He said there has been a Lake County Soil & Water Conservation District project to intensively trap rusty crayfish on the edges of the Boundary Waters Canoe Area Wilderness where they haven’t yet been established, with the goal of limiting their numbers and catching the larger crayfish – thereby allowing the native bass population to feed on the smaller ones and keep them in check.
“We understand we’re not going to remove them from an area short of poisoning everything, but maybe we can take away their competitive advantage over native crayfish,” he said.
A healthy muskrat population could serve as a natural check on the rusty crayfish as well. Passe said researchers are seeing a defined line of where rusty crayfish were and where the traps are getting chewed up by muskrats looking to snack on the crayfish. Otters will also prey on the crayfish. The existing rule curves in the Rainy-Namakan basin, which define water level targets throughout the year by dam managers, have not been working out well for muskrats, which run the risk of freezing to death each winter.
While officials in Canada and the United States are hoping that zebra mussels won’t make their way into Lake of the Woods from Lake Winnipeg or Lake Superior, Passe said the chemistry there may make it difficult for the mussels to take over the lake as they have other water bodies. The low calcium content in the lake could make it difficult for mussels to develop their hard shells, which may end up serving as a natural barrier. Studies haven’t been able to pinpoint what calcium concentrations are suitable for zebra mussels, so in the end prevention is still more important than relying on lake chemistry to stop these hard-shelled invaders.