This stick, taken from the waters of the Sheyenne River on April 2, 2022, shows just how quickly and pervasively zebra mussels have infiltrated the watershed, having just been detected up river on Lake Ashtabula in 2019. Simonson Photo.
By Nick Simonson
Aquatic nuisance species (ANS) have become one of the biggest concerns facing the health of recreational fisheries throughout the country and throughout North Dakota.
Whether it’s the spread of zebra mussels introduced from far away waters in Europe and Asia into lakes throughout the upper Midwest, including those in the Roughrider state, or the invasive silver carp which leap from the water and displace gamefish species in the James River throughout South Dakota and into North Dakota, the impacts of ANS are notable and their future effects on fishing could be disastrous. In an effort to prevent further spread of these species and others, the North Dakota Game & Fish Department (NDG&F) is continuing its programs to detect invasive species early and help educate anglers and all sportsmen about how they can help in 2022 and the future.
Turning Tide of ANS Transport
“We sample over 200 waters a year, and this is specialized sampling for aquatic vegetation [and] crayfish. We pull these large plankton tow nets to look for zebra mussel veligers in a lot of our waterways. We do that on 150 waters,” explains Ben Holen, NDG&F ANS Coordinator, adding, “for North Dakota watercraft inspectors, we’re going to have around 12 to 15 guys this year stationed out of Valley City, Jamestown, Bismarck, Devils Lake, Riverdale and then a few access sites on Lake Sakakawea.”
Holen notes that last year in water access surveys of anglers visiting Devils Lake, roughly eight to 11 percent of boats entering the water on a given day had last launched on a lake with known populations of ANS. Roughly two percent of those boats, or one in every 50, had been on an ANS-infested water within one week of their launch on Devils Lake.
Even at these numbers, the chances of transferring invasives from the state’s smaller lakes with ANS present to the premier fishing destination of Devils Lake are heightened and those impacts could be seen in a matter of seasons, as has happened on medium-sized reservoirs such as Lake Ashtabula in eastern North Dakota. There a discovery of zebra mussels in 2019 has now developed into widespread accumulations of them on debris and docks up and down the reservoir and in the Sheyenne River below it, which isn’t surprising, given that one female mussel can produce hundreds of thousands of offspring a year.
“Anytime you introduce a new species into a waterway, it can have major ecological impacts. Something like zebra mussels, they spawn very quickly. One female can reproduce up to a million eggs in a single year. So, it doesn’t take long after the initial introduction, to two, three or four years after, that they’re covering every surface in a lake.” Holen explains.
Once established, zebra mussels filter water like few other creatures, removing vital phytoplankton from the water column and depositing the waste and nutrients on the lake floor. Through the general clearing of the water, and the development of a rich, nutrient-laden lakebed full of their waste, weeds can grow deeper in a water body, choking out previously fishable depths for bass and walleye, and allowing smaller fish such as bluegills, crappies and perch to overpopulate and later stunt their sizes within the population, altering the fishery permanently.
Zebra mussels aren’t the only destructive invasive species that anglers should be on the lookout for.
“We’re always keeping track of invasive carp on the James River system. We have bighead, silver and grass carp there. Those silver carp are what people see on the news jumping out of the water and they can injure anglers, so we’re always looking at the population making sure it’s still in low densities and just monitoring it yearly for any changes,” Holen explains, adding that the roster of invasive species of concern is growing, “there’s a bunch of other species that we have on our radar: rusty crayfish, Chinese banded mystery snails, starry stonewort, brittle naiad, black carp, New Zealand mud snails, faucet snails, the list keeps going on and on.”
Sportsmen Can Slow Spread of ANS
Whether it’s following the simple four-word instruction of “clean, drain and dry,” for those boats coming out of a water affected by ANS or taking immediate action by spraying a watercraft down with hot water exceeding 140 degrees Fahrenheit for more near-term deployment, the NDG&F relies on sportsmen to help curb the spread of ANS into and around the state.
Hulls treated with hot water, and livewells and internal baitwells sprayed with 120-degree water for two minutes or more will generally be free of any microscopic hitchhikers such as the larval veligers of zebra mussels or fragments of invasive aquatic plants which can regrow elsewhere. If a boat can’t be cleaned, the NDG&F recommends five-to-seven days of drying before re-launching after use on an ANS infested lake. Even before those efforts, Holen explains that inspecting watercraft at the time they’re loaded from the lake is where the spread of most ANS species can be thwarted.
“Boaters when they come off the water they can do the exact same thing that our inspectors do out there on the landscape. So you’re looking for visible vegetation, mud, plants or anything on your boat. You’re removing that at the boating access site,” Holen comments, “we’re extremely fortunate to have such few waters with ANS here in North Dakota, so we really want to keep it that way. It’s very important before and recreation to take the little steps it takes to do things the right way.”
More information on waters in North Dakota where ANS are present, and the types of invasive species anglers should be on the lookout for can be found at: gf.nd.gov/ans.