News and Blog Updates

MAISRC to Study AIS Impacts on Walleye

The Minnesota Aquatic Invasive Species Research Center (MAISRC)’s mission is to develop research-based solutions that can reduce the impacts of aquatic invasive species in Minnesota by preventing spread, controlling populations, and managing ecosystems; and to advance knowledge to inspire action by others. The Center was created in 2012 under the University of Minnesota in collaboration with the Commissioner of Natural Resources (DNR) and with appropriated funds from the Minnesota State Legislature.

One of MAISRC’s new projects, led by Dr. Gretchen Hansen, is aimed at quantifying the impacts that invasive zebra mussels and spiny waterflea are having on food webs and growth rates of fish in Minnesota’s nine largest walleye lakes. The project will use stable isotopes to examine what walleye are eating, where in the lake they’re finding food, and at what trophic level they are eating. Researchers will also evaluate the growth rates of young fish to establish the impact invasive species may be having.

“We know that invasives like zebra mussels and spiny waterfleas reduce native zooplankton and have an impact on the food webs in these lakes,” said Hansen. “What we don’t know is whether walleye and other game fish are able to adjust to find new food sources, or what makes one walleye population more adaptable and successful than another.”

Over the course of this and next summer, researchers will gather samples of zooplankton, invertebrates, and fish from Cass, Red, Kabetogama, Rainy, Vermilion, Lake of the Woods, Leech, Winnibigoshish, and Mille Lacs, which are at varying stages and combinations of invasion from spiny waterflea and/or zebra mussels. Red Lake is currently not infested with either species.

In addition to evaluating the food web impacts on adult walleye, researchers will examine growth rates of juvenile fish to better understand how they are impacted by, and respond to, these invasions.

“Quantifying how these AIS are disrupting the walleye food web will allow managers to set realistic goals and implement policies that could improve the fisheries in the future,” added Hansen. “It’s critical that we understand these relationships between species so we can better manage lakes.”

For more information on this project, visit the MAISRC website. [Adapted from August 2017 MAISRC newsletter article “New project launched to determine impacts of AIS on walleye.”]

[Note from Lake County SWCD: Although the walleye study is being done at the “Big 9” in Minnesota, it has implications for smaller Minnesota lakes as well, including many of the deeper lakes in Fall Lake Township and the Ely area. Lake County SWCD is working with MNDNR Fisheries to conduct smaller scale food web studies on fish in Dumbbell Lake and looks forward to lessons learned at Lake Vermilion and across the state.]

Photo Credit: Spiny water flea on fishing line, Darren Lilja, Lake County SWCD. 

Crayfish Tank

Crayfish #5 Hanging out in the tank

Lake County SWCD has a crayfish tank in the Two Harbors office. Crayfish were collected during the 2017 season from the White Iron Chain of Lakes. The tank serves as a repository for animals needing further identification. Additionally, it provides live specimens for outreach and education, prompting interesting discussions in the office.

Note white Branchiobdella on the crayfish carapace

A few weeks ago, we noticed the crayfish had small white worms attached to their carapace (shell). The white worms are citellate annelids (or intermediaries between oligochaetes and leeches) in the order Branchiobdella. These “worms” attach to the crayfish with suckers. The scientific community has not reached a consensus about the relationship between the citellate annelids and their hosts – some say the relationship is parasitic, some say mutualistic. The Branchiobdella clean the crayfish’s gills, feeding on host tissue. This either benefits the crayfish by providing a “cleaning service,” or it harms them by causing constant wounding of the gills, resulting in infections and bleeding in the branchial chamber. There are no known methods of control for infected crayfish, although the Branchiobdella do seem to be geographically limited to the Northern Hemisphere. Crayfish in the SWCD office are occasionally taken out of their tank and rubbed to remove some of the Branchiobdella. Cleaning the tank and replacing water on a regular basis helps keep the population of Branchiobdella lower as well. Crayfish in the office are also fed regularly with a crayfish food pellet mix including meat, aquatic vegetation gathered in the field, and lettuce or other vegetables.

Showing us who is boss

Most crayfish do not necessarily “play nice” together in the confines of a tank. There are currently 9 crayfish at Lake County SWCD, numbered so we can see how various territorial fights ensue. Stop by and see which crayfish you’ll put your bets on! Feel free to bring some lettuce or other food for the crayfish – they will eat most anything!