Trout Lake Research Rewind: Catching & Counting Invasive Rusty Crayfish

by Riley Steinbrenner

Week Five

It’s that time of the summer when independent, undergraduate research projects are underway! For my housemate, UW biology undergraduate Matt Chotlos, invasive rusty crayfish has been the focus of his. Rusty crayfish are finicky little creatures that have wreaked havoc on many Wisconsin lakes since their invasion in the mid-20th century. According to Live from the Lakes, they destroy plant life that serve as aquatic habitats and they feast on fish eggs of popular pan fish such as pumpkinseed and bluegill.
In 2001, TLS students and the Wisconsin Department of Natural Resources (DNR) began trapping the crayfish in Sparkling Lake—a Long-Term Ecological Research lake funded by the National Sciences Foundation. While they caught harmless, native crayfish as well, only the invasive rusty crayfish were removed from the lake. In addition, the DNR tightened its regulations on the total daily bag limit—or daily amount of fish—for walleye and smallmouth bass that an angler is allowed to catch and remove from the lake. These two fish are known predators to juvenile rusty crayfish, so an upkeep of their population could help remove the invasive species in junction with the trappings, as noted in this article published in 2006 on the UW’s website.
Flash forward sixteen years later, the seven-year-long project to remove rusty crayfish from Sparkling Lake has stopped, as responsibility for sustainable control of the species has shifted to predator fish such as pumpkinseeds and bluegill. Although researchers at TLS did not completely eradicate the invasive species from the lake, it was enough to allow aquatic plants and native crayfish populations to rejuvenate.
By using the same trapping technique as used over a decade ago, Matt—with the help of fellow UW biology undergraduate Ishita Aghi, his partner in the bass-walleye graduate research project this summer—plans on counting the number of native versus invasive species of crayfish he catches in the same locations the invasive crayfish were trapped and removed around Sparkling Lake from 2001-2008. Instead of removing the invasive species, however, he releases them as not to ruin his own data throughout the summer.
In total, 96 traps occupy the perimeter of Sparkling Lake’s littoral zone—which stretches two to three feet from the shoreline—with a cluster of about five to ten traps per site. Matt and Ishita retrieve and count the number of both native and invasive crayfish in each trap every Friday, and refill the traps with beef liver every Wednesday. Although only a few weeks into Matt’s project, the pair have noticed large quantities of the harmless, native crayfish trapped in comparison to the invasive rusty crayfish. Overall, Matt hypothesizes he will observe a low-population density of rusty crayfish in Sparkling Lake throughout the summer in comparison to the population pre-2001, a promising sign of sustainable change in improving the lake’s ecosystem spearheaded by the initial removal project over ten years ago.
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