Northwoods Lake Research Shows How Angler Catch Rates Can Stay High, Abruptly Crash

Jul 2, 2020

University of Notre Dame PhD candidate Colin Dassow with a bass on Crampton Lake.
Credit Ben Meyer/WXPR

Northwoods fishermen and women love when the fish are biting often, offering excitement with every cast.

Frequent catches mean the fish population in a lake is doing well.

Right?

Maybe not.

New research shows, in many lakes, the fishing stays good until it abruptly collapses.

Crampton Lake in Vilas County, which is fully surrounded by 7,500 acres of the University of Notre Dame Environmental Research Center.
Credit Ben Meyer/WXPR

That research largely belongs to University of Notre Dame PhD candidate Colin Dassow, whose days of research can sometimes feel more like recreation.

“I fish for work,” Dassow said. “I do this eight hours a day, sometimes.”

On a cloudless day, he navigates his boat on Crampton Lake in Vilas County, a private lake fully within Notre Dame’s 7,500-acre Environmental Research Center.

Dassow grew up in Wisconsin, and he grew up fishing.

During that time, he gained what seemed like common knowledge.

“Growing up, and I think most people would agree, you assume that if you go out and you catch a lot of fish, that there’s probably a lot of fish in the lake,” Dassow said. “If you do that for a whole summer and you’re catching a lot of fish every time, you assume there’s probably a lot in the lake.”

The logic seems simple.

“Yeah, it makes sense, intuitively,” he said.

But, as it turns out, intuition doesn’t always match reality.

Dassow and his partners set up a study on Camp Lake, also in Vilas County, which has a population of about 350 bass.

During the nights, they started gradually removing fish from the lake by electrofishing, a process that temporarily stuns the fish so they can be moved.

During the days, they took out their rods and reels, fishing two hours each morning and afternoon.

The researchers recorded every fish they caught before releasing it. They sought to test if that common knowledge about catch rate and fish population was true.

“If the number of fish you catch is an indicator of number of fish in the water, then we should see that, as we bring the population down, our catch rate should go down in unison,” Dassow said.

Colin Dassow.
Credit Ben Meyer/WXPR

Instead, the fishing stayed good, even as they manipulated the population down steadily.

Dassow’s crew of anglers remained successful for weeks.

“We were fishing along, and were like, ‘Wow, it doesn’t seem like there’s that many left, but we’re still catching them.’ Then, one day, we went out there, and we had three people out there fishing for two hours. Every day, we were going, and we were catching fish every day,” he said.

“This one day, they went out there, and they caught one fish between all three of them over two hours. We were like, ‘I think this is it.’”

The fishing stayed steady until there were only about 40 fish left in the lake. Then, the catch rate crashed.

It’s a concept called hyperstability.

“I think it might be something that’s going to be new or novel to anglers,” said DNR fisheries researcher Greg Sass, who worked with Dassow on the study.

DNR fisheries researcher Greg Sass, right, with Notre Dame's Stuart Jones.
Credit Ben Meyer/WXPR

Fish tend to cluster in areas of lakes with good habitat.

Fishing there can lead to good catch rates, even as the overall fish population declines. Plus, modern fishing equipment and technology can make fish easier to find and catch.

“We’ve got the latest and greatest baits and technologies as far as rods and reels. That’s very different than it has been in the past, where it might have been, ‘line up this fishing spot between the birch tree, somebody’s dock over there, and the greenhouse,’” Sass said.

Those factors can lead to what the researchers saw: a long plateau of good fishing, then a sharp crash.

“Those catch rates can remain high or stable for a long time until those fish densities get really, really low. Sometimes, it’s too late, at that point, when those catch rates start to decline,” Sass said.

“You can push a population really close to collapse before you realize it,” Dassow agreed.

University of Notre Dame researcher Camille Mosley, standing, fishes with undergraduate Ana Lopez.
Credit Ben Meyer/WXPR

As Dassow continued fishing on Crampton Lake, he came alongside Camille Mosley’s boat.

Mosley, another Notre Dame researcher, is a long way from home, but has similar interests.

“I grew up on the Gulf Coast of Mississippi,” she said. “The Gulf of Mexico is right there. Fishing is important economically, for recreation, and socially.”

This summer, Mosley is building on Dassow’s research, studying the effects of submerged trees and branches on fish populations.

“Bass use habitat differently at different life stages. The [young-of-the-year] use the coarse woody habitat for refuge and the adult bass use coarse woody habitat for forage arena for small fish. We want to add habitat to a lake and see how that changes the population,” she said.

“We’re thinking providing extra habitat should increase, or help, that population of young-of-the-year bass.”

Colin Dassow with two bass in hand.
Credit Ben Meyer/WXPR

Mosley’s data collection is near-identical to Dassow’s: hours of rod-and-reel fishing.

Each catch is recorded thoughtfully.

Dassow hopes sport anglers give similar thought to how they’re fishing in their favorite lake.

“Even if you have good intentions and you’re an angler, it’s really easy to overexploit a population if you’re harvesting it,” he said. “You’re going to keep catching fish even though there’s very few left.”

Maybe vary which lake you visit a little more, Dassow said.

You never know when good catch rates might just be a mirage.