A new way of combating invasive smelt is meeting with mixed success – literally – at the end of a two-year study. The Crystal Lake Mixing Project was able to get rid of most of the smelt in Crystal Lake…but not all of it.
The mixing project began two years ago at the University of Wisconsin Madison’s Trout Lake Station. Its main goal was to stir up the layers of Crystal Lake, warming the bottom and making it inhospitable for cold-water-loving smelt, which were harming native populations of walleye and yellow perch.
To mix the lake, researchers relied on large trampoline-like contraptions that slowly churned up the layers of lake water.
Graduate student researcher Emily Heald says over the course of two summers, the devices successfully warmed the bottom layer of water from 45 to 72 degrees Fahrenheit.
“And so what we found, prior to the manipulation about 40 percent of the smelt population died every year, that’s just the natural rate of mortality," Heald explained. "What we found with the mixing is that we were able to induce a significant mortality rate in the smelt, and we raised it from 40 to 90 percent.”
Ninety percent is a major reduction in smelt numbers, but the mixing didn’t completely eliminate the population as predicted, meaning the fish could rebound in numbers now that the mixing has stopped. Heald says that in itself is an important finding, because it implies that smelt have a greater temperature tolerance than originally thought.
“Now we know that we have many more lakes in Wisconsin that have the habitat smelt do require," Heald said, "and now we can place an even higher importance on preventing the spread of smelt into other Wisconsin lakes.”
Heald says it’s possible the mixing technology could be used in conjunction with another management approach to fully eradicate smelt from a lake. Researchers will continue to monitor what happens to the remaining fish populations in Crystal Lake.