Trout Lake Station, a field station in the Northern Highlands Lake District, contains decades of data about lakes in Northern Wisconsin. This data revealed a hopeful trend in the population of invasive rusty crayfish in the region.
Operated by the Center of Limnology at the University of Wisconsin, Trout Lake Station reveals long-term trends in aquatic ecosystems. Gretchen Gerrish has been the director of TLS since 2019.
“We are a water research field station,” Gerrish said. “We’re here year-round and do mostly research on lakes and shorelines and the lands immediately surrounding lakes … providing knowledge and research on the region’s waters is a big part of what we do.”
Since 1925, TLS has provided support for environmental and limnological outreach, training and research efforts in the area. It provides gear, access to most aquatic sites in the area and sites for long-term data collection.
Gerrish said the station ensures the safety of the researchers through training and gear, and they have weekly seminars with everyone working on the station to develop a “strong research community.”
Along with supporting researchers working at the station, TLS also participates in outreach efforts in surrounding communities. Gerrish said these outreach efforts include events at the station, art and science programs, going to schools in the area or bringing students to the lab for activities.
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The long history of the station’s operation offers a rare opportunity for long-term ecological studies. Researchers have sampled the lakes since the station opened, according to Gerrish.
“It’s pretty unique to have 100-year numerical values with tools that we’re still using today being shared and compared,” Gerrish said. “And so that’s one of the benefits … Everybody now wants long-term data, right? But the visionaries of the past were able to build that and now [we are] able to look back that long ago, [which] is really pretty incredible.”
One of the projects that benefited from the long-term data collected at the lakes around TLS is invasive species research into rusty crayfish.
The importance of invertebrates to the ecosystem is often overlooked, Gerrish said. The rusty crayfish reshaped the ecosystem when they reached a large population.
Ph.D. student Danny Szydlowski at UW researches the causes of environmental changes in Wisconsin lakes. He led the latest data collection for the rusty crayfish research project in 2020 during his time as a master’s student at the University of Illinois.
Szydlowski said the Ohio River Basin is the native habitat of the rusty crayfish, and they were likely introduced to Northern Wisconsin lakes as bait for fishing.
Rusty crayfish are more aggressive and have larger claws than the native crayfish, allowing them to outcompete the native crayfish and to reach very large population sizes, Szydlowski said.
“One of their favorite foods is aquatic bugs, so they’ll really cause declines in those numbers, which is bad for the whole food web,” Szydlowski said. “And basically they’re an organism walking around with clippers for hands, so as they’re rooting around, they’re destroying all the aquatic plants, as well.”
The rusty crayfish have been researched in this region since the 1980s, but long-term observations of an invasive species like this study are not very common, according to Szydlowski.
Long-term research is important to see ecological trends. Szydlowski said many studies on invasive species are done on short time spans and often at the peaks of these invasive species.
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Continuity of procedure is important to obtain relevant and useful data, and that is something TLS researchers provide, Gerrish said.
“We would go to all these different sites in the lakes that had been sampled in 1987, 2002 and 2011, and I had talked to some of the folks who did that research in the past to replicate their methods exactly to keep everything standard over time,” Szydlowski said.
This long-term study indicated an unexpected trend in the rusty crayfish population. Szydlowski said over the past 10 to 15 years, the number of rusty crayfish in many of the lakes has been declining.
The decline has occurred naturally without human involvement, which is rare to observe in invasive species, according to Szydlowski.
“In most cases, they only decline with a lot of intensive human management, but this is one of the first cases of a natural decline,” Szydlowski said. “And what’s even [more] rare is we were able to show then that the plants and to some degree like snails that they were feeding on have started coming back, which is really hopeful story.”
