Plentiful walleye contribute to the magnificent recreational opportunities at Voyageurs National Park. However, aquatic invasive species, such as zebra mussels and spiny waterflea, threaten the health and growth patterns of Minnesota's state fish.
The NPS, Minnesota DNR, and University of Minnesota collaborated on an extensive study that measured walleye growth in large lakes infested with zebra mussels and spiny waterflea. The researchers focused on nine large Minnesota lakes - including Rainy and Kabetogama - and found that the presence of these two invasives significantly impacted the growth of young walleye:
“Walleye were smaller at mid-summer and grew more slowly throughout the growing season… resulting in mid-August lengths that were 15 and 18 mm (12 and 14%) smaller in lakes containing Bythotrephes and zebra mussels, respectively, compared to uninvaded systems” (Hansen et al., 2020).
Lakes with higher amounts of AIS have reduced zooplankton levels. Since walleye rely on zooplankton as a food source during their first year of life, the researchers believe this could be impacting walleye growth. These findings are especially concerning since survival over the first winter is lower for smaller first year walleye. However, there may be other impacts on the walleye growth, such as increasing water clarity. Hansen plans to continue researching the impacts of AIS on walleye growth with smaller to medium-sized lakes.
For more detail read the Star Tribune, Quetico Superior, and Minnesota Public Radio stories on this paper.
Read the full paper "Walleye growth declines following zebra mussel and Bythotrephes invasion," published in the journal, Biological Invasions.
Photo by Susan Potter
