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Sustainable Aquaculture and Seafood: Long Trawl Yields Big Data Haul for Lake Whitefish

By Aaron Conklin, Wisconsin Sea Grant

Sixty-five days. Nine weeks. Two-plus months. Really, any way you cut it, it’s a lot of time to spend on a boat, collecting and counting fish.

But that’s how Titus Seilheimer, Wisconsin Sea Grant’s fisheries outreach specialist, spent large chunks of his time over the past year, in the service of a research project aimed at determining the effects of the use of lake whitefish trawl nets by commercial fisheries in a specific area of Lake Michigan. The fish are traditionally harvested using trap nets.

Lake whitefish represents Wisconsin’s largest commercial harvest, more than 1.5 million pounds in 2012, according to the most recent figures from the Wisconsin Department of Natural Resources (WDNR). The value of the catch is roughly $3 million annually.

Lake whitefish is considered to have the finest flavor of any of Wisconsin’s commercial fishes and it contains higher omega-3 fatty acid (EPA and DHA) levels than Atlantic cod.

Working with the Susie Q Fish Co. on a midsize trawler, Seilheimer surveyed these omega-rich catches collected by a whopping 491 drags over those 65 days, tabulating the whitefish and the bycatch and tagging certain fish for tracking purposes and survival estimates.

Seilheimer was surprised by the lack of actual bycatch. Over the 65-day study period, the amount of bycatch landed less than 3 percent.

That’s a potentially critical finding for the future of whitefish trawling in the Two Rivers/Manitowoc area of Lake Michigan, a practice that’s currently not allowed under state law. (The WDNR granted special approval for the trawling study in this region.)

In the 1980s, trawling for alewife and smelt, along with experimental trawling, resulted in both heavy bycatch and bycatch mortality. Preliminary results from Seilheimer’s study indicate that changes in the lake, such as increased water clarity, may be a factor in the changes in bycatch.

The study’s early and long hours weren’t the only challenging aspects of this particular research project. Turns out wrangling and tagging sizable lake trout by hand isn’t as quick and easy as it looks.

The other Herculean aspect isn’t quite so piscine—it’s the magnitude of the data Seilheimer collected. He now has figures charting everything from the number of whitefish caught in each month to the size range of the lake trout in the bycatch and where some of those lake trout went after being released. One tagged lake trout was eventually discovered more than 300 miles away in the Canadian waters of Lake Huron.

While the first round of data collection is now complete, the trawling project will continue into a second year, this time featuring trawls at depths that are natural rather than experimental. The study trawler now has a video camera system installed to monitor the catch and bycatch.

“I’m glad we’re going to be able to continue this research,” said Seilheimer. “It’ll just be without me on the boat so much.”

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