Siscowet Trout: A Plague of Riches
After sampling a variety of holiday dishes and desserts, you might feel like you've had too much of a good thing. You are not alone; people involved with Lake Superior's fisheries are also looking abundance in the eye. Despite Lake Superior's chilly temperatures and relatively low productivity, researchers and fishermen think the lake might have too many fat fish.
Not just any Lake Superior fish can sport up to 70 percent body fat. It's siscowet, a hefty lake trout that swims with burbot in the deeper waters of Lake Superior.
"'Siscowet,'" said James (Jim) Kitchell, professor of zoology at the University of Wisconsin-Madison, "literally translates from Ojibwe to 'cooks itself,' which is what happens if you put this fish near a flame."
Unlike their svelte kin (namely lean lake trout), obesity is a natural state for siscowets. Siscowets' tendency to develop more body fat (40-70 percent) than lean lake trout (about 10 percent) is natural and not a source of concern. What fisheries researchers and those catching fish out on Lake Superior have noticed is that there are copious numbers — about 100 million according to one estimate — of these plump native fish.
"If the goal of fisheries management was to restore native fish in Lake Superior, then siscowets are a huge success," said Kitchell. "We've got riches! If the goal is to restore an ecosystem that supports important recreational and commercial fisheries similar to those of the past, then we have a plague — a plague of those riches."
In two lively talks entitled, "It's a Fish-Eat-Fish World," hosted by Minnesota Sea Grant in October, Kitchell explored the predator-prey dynamics in Lake Superior. He focused on the hefty siscowet population and its impact on the lake's food web. Duluth and Grand Portage, MN, audiences both enjoyed Kitchell's fish tales.
"Siscowet among smelt are like sharks among schools of tuna," Kitchell analogized. "Introduced smelt might have played a role in displacing native herring but now that they are being eaten by a sizable lake trout population, the chances that herring will recover has improved."
Kitchell noted the decreased number of smelt ("T-bone steaks from a siscowet's perspective") since their hey-day along the North Shore. Smelt are the preferred food of Lake Superior's top predators (lake trout and burbot) but as smelt populations decline the big fish are forced to eat Mysis (a freshwater shrimp), which in Kitchell's words "are cheese sandwiches and simply not as satisfying as a T-bone steak."
The Hendrickson family, who has operated a commercial fishery on the North Shore for over 100 years, reports that trout fishing is the best it has been in a lifetime. But there isn't much value in having a siscowet on the end of the line or in the net. They try to avoid catching siscowets by not casting their nets as deeply, so that they catch lean lake trout instead.
"People generally don't eat siscowet and, although their omega-3 oil content might interest folks in the health supplement industry, there just isn't a demand for these fish," said Jeff Gunderson, associate director and fisheries extension educator for Minnesota Sea Grant. "We're exploring opportunities to market siscowet and the economics of using them for their oils, but so far they're a tough sell."
Kitchell credits effective constraint of commercial fisheries and persistent sea lamprey control for the successful recovery of Lake Superior's lake trout. "Looking at what has happened in the lake and the results of computer simulations, it is clear that lamprey control needs to continue if Lake Superior is to keep its lake trout."
He delivered three parting comments as he left the Minnesota shores of Lake Superior to return to Wisconsin:
1) "It is imperative that people understand what is going on in the Great Lakes;"
2) "We must maintain control over the sea lamprey;" and
3) "Lake Superior folks should take a bow because this is the only lake that is accomplishing the goal of restoring native fish species."
If you are interested in hearing Kitchell's presentation, visit the speaker series webpage. His talk was part of the "Superior Science for You!" speaker series made possible by a grant funded under the Coastal Zone Management Act by NOAA's Office of Ocean and Coastal Resource Management in conjunction with Minnesota's Lake Superior Coastal Program.
A full schedule of the series and descriptions of the talks are available on the Web site mentioned above, or you can contact Minnesota Sea Grant at (218) 726-7677 for more information.
By Sharon Moen