Stun, collect, study: electro-fishing advances understanding of fish populations in Northwoods lakesSubmitted: 07/31/2015

Ben Meyer
Managing Editor / Senior Reporter

BOULDER JUNCTION - The boat looks like something from a science fiction movie as it creeps across Northwoods lakes at night.

Its long arms jut into the water, sending electrical pulses into the lake.

Under a nearly-full moon on a warm July night, it motors across Sparkling Lake in Vilas County.

"We can actually sneak up on them in the evenings, when it's dark out," says Dr. Noah Lottig, who's driving the boat. "They're up there, they don't see us coming, and we can sneak up on them."

This is how Lottig fishes. He's an Assistant Scientist at the UW-Madison Trout Lake Research Station in Boulder Junction. The electrical field produced by his boat is the first step.

"It temporarily stuns the fish, allowing us to collect the fish [and] put them in a live well in the boat," Lottig says. "I want to make sure that we have enough [electricity] to stun the fish, but not so much that we have the potential to hurt them."

It's a ritual that Trout Lake Station scientists perform every summer.

"We've been doing this for 30 years," Lottig says.

As part of the Long Term Ecological Research program, scientists record information on the fish they stun and collect, helping to find trends in population, diversity, and fish health.

"We're interested in understanding long-term change in lakes," Lottig says. "One of the things that we study is long-term change in fisheries communities."

Lottig, helped by a handful of undergraduates on board, sticks to routes near the shore of Sparkling Lake. At night, fish tend to gather in this area. As the boat passes over them, the electrical field stuns them for a moment. Two undergraduates wait in the front of the boat with nets on poles.

"If you see a fish, get it, grab it right away, as fast as you can, and pull it out," Lottig instructs them.

Their opportunity is short.

"(The fish) recover remarkably fast. Sometimes seconds," Lottig says. "There's very, very low mortality. I've been doing this five years, and it's at least three or four years since we've lost a fish doing this, so our mortality is extremely low."

After 30 minutes, Lottig's team carefully records the length and weight of their catch. The team collects scales from some of the fish. He fishes for three sessions of 30 minutes, and collects everything from panfish to smallmouth bass to perch before throwing them back.

The information they record goes into the long-term record of Sparkling Lake. In this particular lake, for example, scientists have been able to track the decline and subsequent rise of panfish populations. It seems to be directly connected to the influx, and later eradication, of the invasive rusty crayfish.

Monitoring trends like this is only possible through this odd-looking endeavor, electo-fishing at night in the Northwoods.

"We got a wide range of species. A couple of the runs, we got a lot of them," Lottig reviews. "We got what we were looking for."

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