Imagine an underwater army of crustaceous lumberjacks chopping down the kelp forests on the floor bed of lakes with their large pincers. This isn’t something out of a science-fiction movie. This is how the Rusty Crayfish, an invasive species from Ohio River Basin, essentially deforested Sparkling Lake in Vilas County, Wisconsin.
They were so abundant that if you sat on the shore, you could see them scuttling around the shallows. About four years ago, a multi-year initiative to rid Sparkling Lake of the Rusty Crayfish proved successful, and today the lake has bounced back.
I met with Gretchen Hansen, a postdoctoral researcher and leader of the project, at Memorial Union. We sat on a bench next to the lake; it was fitting that the Center for Limnology, where Gretchen spent a part of her undergraduate research and a large part of her graduate research, sat just a few feet away.
Hansen started her research on the crayfish at the Center for Limnology when she was an undergraduate at the University of Wisconsin-Madison.
During her time as a Ph.D. student, Hansen returned to crayfish research in 2008. Sparkling Lake, the location of the research, is one of seven lakes under a long term monitoring system. In 2001, researchers decided it was time to rid the lake of the Rusty Crayfish. By chopping down the fauna on the bottom of the lake, the crayfish removed locations for smaller fish to hide from predators. The crayfish also contributed to the steep decline in native aquatic insects and fish.
The research team removed the Rusty Crayfish with a two-pronged approach. The first part, and also the least glamorous, involved trapping the crayfish using metal funnels with beef liver bait.
According to Hansen they used “anything sticky and gross” to catch the crayfish. At the beginning of the summer, a typical haul was thousands of crayfish per day. By the end of the summer, they emptied the traps infrequently and only hauled in about 30 a day.
I naturally wondered what they did with the crayfish after they caught them. The answer? They had crayfish boils. Hansen recalled the crayfish being delicious and tasting like lobster.
In the second segment of their project, the researchers changed fishing regulations so there would be less removal of predator fish like small-mouth bass. It appears humans and small-mouth bass have something in common: They both enjoy a good crayfish.
“The hardest part of the job is working on a whole lake that has so many components and making a cohesive story,” Hansen said.
Hansen’s team initially hypothesized that if they removed the crayfish, they would see an increase in the insect population. However, no increase was observed.
The best hypothesis they came up with to reason the stagnant insect population was that fish began to insect larvae instead of crayfish.
Hansen looked chagrined as she said this but she explained how science and research is unpredictable and if it weren’t, it wouldn’t be interesting.
Hansen currently works for the Wisconsin Department of Natural Resources. She said invasive species continue to be a problem in Wisconsin and around the nation, and she doesn’t foresee that changing anytime soon.
But every cloud has a silver lining. Most invasive species establish slowly or have very little effect, like sparrows. Unfortunately, the ones that do establish wreak havoc on their ecosystem of choice.
Hansen explained prevention and education are far easier than post-arrival removal of invasive species. It is impossible for the government to watch every boat that goes into the water and therefore, people must be educated to do the safe -guarding themselves.
Today, Sparkling Lake is still sparkling but with significantly fewer crayfish.
“The residents really noticed a difference as their kids aren’t afraid to swim in the lake anymore,” Hansen said.
Although the insect population hasn’t increased, there is a trade-off: The numbers of other native fish species, like the pumpkinseed gill, have bounced back from nearly zero.
Will the crayfish army make a comeback in Sparkling Lake in the near future? Nobody knows but they have been held at bay so far.