Volume 3 2015


A Long Trawl

At least one day each week since the beginning of February, Sea Grant’s Titus Seilheimer has hopped aboard the midsized fishing boat Peter Paul and headed out onto the always beautiful and sometimes treacherous waters of Lake Michigan, there to trawl for whitefish.

No, he hasn’t taken up fishing for a living.

He’s counting bycatch rates.

Seilheimer’s working with a Lake Michigan commercial fisherman on a study to determine whether using trawl nets to collect whitefish—a practice currently not allowed under state law—can be done effectively without adversely affecting key non-target species such as salmon, trout and walleye. The boat is trawling in a limited area expressly approved for trawling study by the Wisconsin Department of Natural Resources (DNR).

Commercial fishers are extremely interested in adding trawl nets to their tool arsenal. Currently, state law allows trawling only for smelt and limits whitefish harvest to gill and trap nets, a limitation that shortens their fishing season by several months each year. Net season now runs from April to October.

“With trawling, these fishers would be able to go out when they want to, when they need to,” explained Seilheimer.

But first, the effects have to be carefully studied, and that’s where Seilheimer comes in.

Among ocean fisheries, trawling can be considered controversial, as the nets occasionally destroy coral reefs and fish habitat. On the Great Lakes, the concerns have more to do with the impact on non-target fish species. Back in the 1980s, the state allowed commercial fisheries to trawl for alewife and smelt. Smelt is still allowed, but both types of trawling resulted in “substantial” bycatch of key fish species, particularly lake trout, said David Boyarski, the DNR’s northern Lake Michigan fisheries supervisor.

“There was also a high mortality associated with that bycatch,” he added.

The mortality was so high in fact, that in 1991, the DNR instituted a rule that required trawlers to use a diverter attachment that redirected larger fish out of the net.

Seilheimer and Steven Kulpa, the Two Rivers-based fisherman Seilheimer is working with on this study, are acutely aware of the bycatch issue—it’s why they’re trying to measure and document it in relation to more modern trawl nets available today.

“Every time we have new fishing gear, it’s important to gauge the impact,” Seilheimer said.

So far, the only bycatch to make an appearance has been small numbers of lake trout and whitefish sized too small to qualify for commercial sale. Seilheimer has been tagging the trout to track the fish’s survival rates after catch.

“The trout tend to do well coming out of the net,” he said. “We’ve already spoken to other local fishers and sport anglers about being on the lookout for tagged fish.”

Because whitefish tend to occupy easily identifiable depths in the waters of Lake Michigan, a significant part of the study involves trawling at variable targeted depths between 100 and 300-plus feet. In addition to counting bycatch, Seilheimer is also recording the water temperature, speed and distance of each trawl.

“It’ll be a lot of data,” he said.

The data capture is only the first step in the process of bringing whitefish trawling to the waters of Lake Michigan.

“This study doesn’t commit us to any future action to allow trawling or to modify commercial fishing laws,” noted the DNR’s Boyarski. Any changes to commercial fishing rules would involve public hearings and the approvals of the state’s Natural Resources Board.

But even if the study doesn’t result in a policy change, it will still have been valuable from a scientific standpoint.

“We catch the fish, we count the fish,” Seilheimer said. “These are real numbers.”

Seilheimer will continue to trawl with the crew of the Peter Paul through the end of the year.

The Aquatic Sciences Center is the administrative home of the
University of Wisconsin Sea Grant Institute & University of Wisconsin Water Resources Institute.

©2011 University of Wisconsin Board of Regents