By Nick Simonson

With the detection of zebra mussel veligers in a summer water sampling from Lake Sakakawea, and subsequent cold water surveys of the eastern end of the reservoir this fall revealing adult specimens of the aquatic nuisance species (ANS), the North Dakota Game & Fish Department (NDG&F) is already undertaking next steps to monitor and contain the invasives now found in one of the state’s largest and most visited lakes, according to Ben Holen, NDG&F ANS Coordinator.

“We collect thousands of water samples from across the state using plankton tows. And those plankton tows are targeted sampling looking for zebra mussel veligers, so the larval offspring. We collect those samples during the summer and then spend the fall time of the year processing the bulk of those samples,” Holen explains of the situation, adding, “unfortunately last week we were going through water samples and we ended up finding a handful of veligers within some water samples taken in August from Sportsman’s Centennial on Lake Sakakawea. That immediately prompted us to do a follow-up survey where we put on wetsuits, went into that cold water of Lake Sakakawea for a few hours in that Sportsman’s Centennial area and we ended up discovering two zebra mussel adults.”

Zebra mussels begin life as near-microscopic veligers, tiny wisp-like larvae which float around in a body of water before sinking to the bottom, attaching to substrate and developing their shells and turning into the now-recognizable adult forms with light and dark striping.  As an adult of not more than a few centimeters in size, just one mussel is capable of filtering more than a liter of water each day, removing plankton and other microscopic food sources necessary for developing young gamefish like walleyes and their prey species, such as the smelt found in Lake Sakakawea, which form the water’s forage base. One adult zebra mussel is capable of producing hundreds of thousands of veligers each year, depending on water quality and location, resulting in exponential growth possibilities.

“It’s very difficult because each lake probably has some different growth rates.  The mussels that we did find were large adults, so that indicates to me that they’ve probably been in there for a while, but it’s hard to say whether they’ve been in there three years or more. It all depends on growth rates. We’re currently looking at potentially getting some of those mussels aged, if we can find someone who’s good that that, and that might give us some more information,” Holen states.

Since 2019, NDG&F has increased surveillance efforts at both Devils Lake and Lake Sakakawea, premier fishing and boating recreational destinations in North Dakota which draw tens of thousands of anglers each summer, and boats from across the United States and Canada. A recent influx of funding has also helped with a larger informational and practical campaign by the agency to help anglers learn how to properly clean, drain and dry their boats to limit the spread of ANS in the state’s waters. Each summer over the past six years, NDG&F was able to hire temporary seasonal workers to monitor and assist boaters at Sakakawea’s boat ramps, however finding consistent and ample staffing was difficult.  Due to the size of Lake Sakakawea, treatment or drawdown to kill zebra mussels is not possible, like on nearby Smishek Lake, where zebra mussels were also recently discovered and treated with chemicals to eradicate a majority of the population.

“With Sakakawea, we found those two mussels a good distance apart, and treatment is really not a possibility at this time. The cost would be too great, and we would likely be very unsuccessful anyways, so it really comes down to mitigating the spread where we can,” Holen explains.

Holen states that the agency will now shift into an adjusted state of awareness and action when it comes to Lake Sakakawea, ensuring that boaters leaving the water are aware of the presence of zebra mussels, and the extra steps necessary to prevent any possible contamination by the species leaving the reservoir and being transported to other waters in the state and across the region. 

“That really is in combination with every water recreationist out there making sure they’re doing the right thing at ramps every single time; making sure they’re clean, drain, dry.  When they’re moving between different ends of the lake, they should consider hot water decontamination before they fish the east side and then move to the west side. We’re going to try to delineate and figure out where this mussel population is in the lake as much as we can. We have done some efforts this fall, to this point we haven’t found any more adult mussels but we’ll hit the ground running and ultimately work with our education outreach team to come up with best management practices,” Holen states as to next steps in the spring to mitigate the spread of zebra mussels from Lake Sakakawea.

For more information on waters where zebra mussels and other ANS are present in North Dakota, along with tips to prevent their spread, visit gf.nd.gov/ans.

Simonson is the lead writer and editor of Dakota Edge Outdoors.

Featured Photo: Zebra mussels can have profound impacts on popular fishing waters where they are introduced, removing the most basic forage items necessary for fish recruitment, changing water clarity, and impacting areas of weed growth due to clearer waters.  Simonson Photo.