In whole-lake experiment, have invasive crayfish met their match?

September 9, 2013 by Adam Hinterthuer, University of Wisconsin-Madison
The numbers of rusty crayfish, an invasive species blamed for decimating fish, insect and plant communities in Sparkling Lake, have dropped dramatically since a UW-Madison experiment concluded. Credit: Lindsey Sargent

Four years ago, UW-Madison researchers wrapped up a multi-year effort to dramatically reduce the population of a destructive invasive species in a northern Wisconsin lake.

Now, a recent survey of the lake shows that not only have fish, insect and plant communities bounced back in Sparkling Lake, but the invasive rusty is on the ropes.

Gretchen Hansen, a former postdoctoral researcher in the UW Center for Limnology and lead author of the study published in the July issue of the Canadian Journal of Fisheries and Aquatic Sciences, says that when rusty crayfish invade a lake, they use their claws to snip right at their roots. Scientists think this lets crayfish better spot approaching predators, but it also removes critical cover for other species, leaving them nowhere to hide from predators like .

In the early 2000s, when UW researchers began the rusty removal experiment, Sparkling Lake was essentially deforested. There were no beds of aquatic plants, no spawning sunfish and tons of invasive crayfish. "Rusties then were crazy abundant," Hansen recalls, adding that crayfish boils were not an uncommon occurrence for the students and other scientists working on the project. "We were catching 1,000 a day and eating them all the time."

Today, researchers are more likely to have a fish fry.

By suppressing the rusty crayfish population, Hansen says, researchers enabled to grow back and, with them, the aquatic invertebrates and fish that called them home. It was an outcome researchers aspired to but weren't sure was possible.

Gretchen Hansen (left) and graduate student Ali Mikulyuk preparing to dive for a plant survey in Sparkling Lake.

Previous studies suggested that many plant species wouldn't regrow from the and Sparkling Lake's were tenuous at best.

"We thought that pumpkinseeds might come back, but we were a little concerned that [bluegills] had been extirpated," she says, noting that from 2000 to 2004, extensive surveys of Sparkling Lake turned up only a couple dozen pumpkinseeds and no bluegills.

Today, says Hansen, now a research scientist with the Wisconsin Department of Natural Resources, rebounding populations of fish like bluegill and pumpkinseed are helping keep rusty crayfish populations down by preying on juvenile crayfish and larvae.

But the news isn't good for all species in the lake, she says. "Sparkling Lake used to have tons of mayfly larvae, but now you can't find any," Hansen says of an invertebrate species that made up a key element of the lake's food web. "We thought they would rebound, but they haven't."

Hansen says this is possibly because fish like rock bass and smallmouth bass switched their diets from crayfish to aquatic invertebrates as the rusties were removed from the food web. The increase in other insect-loving fish like bluegill only made things worse for the mayflies.

"Things are often more complicated than you might expect," Hansen says. "But it's a transient thing, and we only know how the lake is now, four years later. That doesn't mean that's what it'll be like in another four years."

For now, Sparkling Lake's native ecosystem is healthier than it's been for decades and a pernicious invader is being kept in check naturally.

As far as fighting the invasive crayfish on other lakes, Hansen thinks that, if the right agency or lake association had the time and money to pay someone to extensively trap crayfish, it could work. But, she cautions, it's a lot of work. Her group needed eight summers of full-time trapping to finally get rusty crayfish numbers where they wanted them.

Thanks to that time and effort, though, the work seems to have paid off. At the very least, Hansen says, "it's pretty tough now to put together a crayfish boil."

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1 / 5 (2) Sep 09, 2013
so the experiment was if it were feasible to simply hunt the invasive species by hand and how long it might take to clear a mid sized lake.

well heck if you have enough money you can pay someone to do anything ... this was an experiment or a government sanctioned safari?
5 / 5 (1) Sep 09, 2013
So, the solution to invasive crayfish is to eat them? Congrats, researchers. Science!
1 / 5 (1) Sep 10, 2013
What am I taking from this? An exotic, invasive species was out of control. Now it's under control, naturally. No more intervention needed. We've discovered it's possible. Now we can investigate ways to do it efficiently.

This criticism, it's like complaining about CERN's electric bill.
1.4 / 5 (9) Sep 10, 2013
Mmmmmmmmm tons of boiled crayfish......

Food Porn... looks up hundreds of recipes....

Boiled, fried, with chillie sauces, smoked, with salad, Mmmmmmmm hold annual cook offs - with fresh crays... Mmmmmmmmmmmmmm 1000 hungry campers, with 5000 nets, for 3 or 4 days over the summer... every summer.....

Google - Images - crayfish recipies = Food Porn.....

Curries, soups, in bread crumbs, asian style foods, Yummy - smart marketing = clear the lakes in no time......

not rated yet Sep 10, 2013

the criticism is, that this was not about discovering if it were possible. If the goal was to see if an invasive species was removed would the ecosystem bounce back fully I would never have commented, even though that has been proven time and time again, but that is not how this article is structured... this article is stating that it is surprising that you can remove an invasive species... which has been known. You can hunt anything and pay people or students to do it and get the numbers under control. This is no new feat, this is no new discovery. This should have been like three paragraphs.

The studies quoted were obviously wrong to think plants would not repopulate an area that they were native to once their predators were removed.
1 / 5 (5) Sep 11, 2013
So... an invasive species could serve as the basis for a whole new industry (crayfish harvesting). Sounds like a win to me.
not rated yet Oct 25, 2013
Actually, this research was about 1. determining if it was possible to remove enough crayfish to allow the native species to recover and 2, assessing if they could then be kept in check by native predators. You seem to think it is obvious that invasive species can be controlled and native species will recover, but it has proven quite difficult to control many invasives once established (to the point that many scientific papers state that there is no point in trying). Further, you say that other studies were "obviously wrong to think plants would not repopulate...". These studies did not "think" that plants wouldn't repopulate - they showed that they would not. This study showed on a larger scale that they could, and furthermore that the plant recovery allowed native fish to increase to the point that they could control crayfish after the trapping stopped. This is how science works - building on the work of others, and replication (or lack thereof) to find answers.

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