March 10, 2014
By Marie Zhuikov
It’s a winter’s night on Lake Michigan. Underwater in the shallows, the eel-like and lowly burbot gather in a brown writhing mass to spawn. With their serpentine bodies and dangly chin barbels, it’s not a pretty picture, but the activity ensures the species’ survival as one of the top predators in the food chain along with lake trout.
Wisconsin Sea Grant scientists have discovered that burbot spawn in deep reefs and also later in the season than previously known. Their findings, recently published in Transactions of the American Fisheries Society, add a fifth spawning behavior to those already identified for burbot.
Burbot, known in Latin as Lota lota from the French word for codfish, are the only species of cod that live entirely in fresh water. Also known as eelpout, lawyer and lingcod, the burbot is prized for its delicate white meat. A popular restaurant on Washington Island off the Door Peninsula, KK Fiske, draws patrons from as far away as Chicago by offering “fresh lawyers” throughout the year prepared fried, boiled, broiled and shish kebabed. However, just as many anglers are put off by the burbot’s eel-like appearance and penchant for wrapping its tail around their arms as they try to unhook it.
For the study, conducted in 2007 and 2008, researchers collected burbot larvae in lakes Superior, Michigan and Huron during spring and summer. While burbot are known to spawn in landlocked lakes and Great Lakes tributaries in winter (January to March), and in rocky shallow waters of the Great Lakes, researchers found burbot larvae at deep reefs in the middle of Lake Michigan and offshore areas of Lake Huron in June through August, signifying that burbot spawn later and deeper than previously understood.
John Janssen, professor of fisheries ecology at the University of Wisconsin-Milwaukee, said the finding was accidental. “We were working on collecting bloater larvae, and we were surprised by the number of burbot we collected on the midlake reef. We were also surprised that we were seeing them in late June. They were really tiny, which means they were just born. This implies there’s a concentration of burbot on those mid-lake reefs.”
Janssen explained that although midlake reefs are deep in the water and away from sunlight, they offer plenty of food for young fish due to their topography and the currents that collect around them. “The abrupt topography concentrates zooplankton. They swim against the current and get deflected upward. Or larger zooplankton, like Mysis, will try to migrate down to their preferred depth and the reef stops them.” This concentrates the food that young fish need to survive.
Janssen said these findings will help fisheries managers in their quest to manage on an ecosystem basis. “Burbot interact with many other fish. They like to eat a lot of sculpins, which are eaten by lake trout, and sculpins eat lake trout eggs. Knowing more about when and how burbot spawn adds more information to figure out the interactions between species.”
The findings could also help with efforts to count burbot. Janssen said that current census efforts rely on trawl nets over soft-bottomed areas of Lake Michigan. “We know now that burbot live on rocky bottoms, which can’t be reached with traditional trawl methods. In terms of understanding how the Lake Michigan ecosystem works, we could go down with a submersible to ground-truth what’s happening with the burbot population,” Janssen said.
Another question that Janssen would like to explore is where the burbot that spawn midlake originate from. “Are they born in streams and then drift out midlake and eventually spawn? Or were they born on the reef, or somewhere in between? That’s a big question that we could probably answer.”