DNR Explorers Make New, Exciting Discoveries on Lake Superior
August 3, 2006
It's the stuff of legends.
"For many years we have wanted to explore the deepest location in Lake Superior and, finally, this year, we were able to do so -- with great results," said Shawn Sitar, research biologist for the Department of Natural Resources' Marquette Fisheries Research Station.
Sampling the deepest hole in the deepest of the Great Lakes was a huge logistical challenge for the team on board the DNR Research Vessel Judy, which includes research technician Helen Morales, Captain Kevin Rathbun and Assistant Captain Brandon Bastar.
Normally, research assistants Greg Kleaver and Dawn Dupras are rigging up lines on the deck of the Judy for setting nets at depths 10 times shallower and 25 miles closer to shore. This time, as the nets released from the back of the boat and drifted slowly on more than a mile of line, there was uncertainty whether the gear would deploy at such depths.
What did Sitar and his team discover? There are plenty of fish in the depths of the big lake.
"About 30 miles offshore, in about 1,330 feet of water, we found an abundance of siscowet lake trout," he said.
Although all of Lake Superior contains deepwater areas, the deepest lies within Michigan's boundary, about 30 miles north of Munising. Nautical charts indicate a huge flat area, averaging 50 feet deep, then a sheer drop off the northwestern edge that bottoms out in a 1,330-foot valley beneath the lake's surface.
DNR researchers were not sure if fish lived in these deep waters and, if so, in what abundance. So, the decision was made to explore the deep spots and consolidate findings.
The study was a collaborative project approved by the Great Lakes Fishery Commission and its technical committee, of which DNR is a long-standing member, along with Wisconsin, Minnesota, Native American tribes, federal biologists and the Canadian province of Ontario.
Lake Superior is cold -- very cold. Its temperature is a constant 39 degrees on the bottom, and there is relatively little light. This environment is ideal habitat for the siscowet, a form of lake trout that Sitar said has adapted over time from the more familiar lean lake trout to thrive in the deep, cold water.
Siscowets are a long-lived fish. Though it is common to find lean lake trout in Lake Superior that are 20 to 25 years old, siscowets typically reach 40 years and more. This fish has larger eyes and fins than lean trout, and, most notably, a much higher body fat content. These adaptations allow it to live in such an extreme environment, where it feeds on sculpin, burbot and other deep water fishes.
Native Americans gave the siscowet its unusual name. In Ojibwa, the word means "cook itself," which refers to the sizzle of the fatty flesh as it cooks over an open fire.
The abundance of fat in these fish is one reason for the study. Siscowet were commercially fished until the late-1980s, when it was found that contamination from PCB-type compounds made the fattier fish unsafe for human consumption.
Today, there is renewed interest to commercially harvest siscowet for fish oil, to be sold as dietary supplements. Pharmaceutical labs have developed an oil extraction process that can filter such contaminants and leave the purified oil that contains omega 3 fatty acids which are beneficial to the heart and arteries.
Ongoing fisheries research to explore the deep waters of Lake Superior will help to determine if renewed commercial harvest of siscowet is sustainable.
Another reason to learn more about siscowets is that it will help us better understand where and when these fish spawn, which, in turn, may provide more information on why the large-scale natural reproduction of wild populations of lean lake trout has been successful only in Lake Superior.
"Native ecosystems self-adapt," Sitar said. "The lake and its inhabitants, vegetative and fleshy, come into a natural balance when not disturbed by new introductions, so with current lake trout populations as good as they are, we do not need to stock on top of this flourishing native species."
The Lake Superior Technical Committee of the Great Lakes Fishery Commission meets this month in Marquette, where all the biologists will report what they have found in their deep water surveys.
The Marquette research team will delight in telling their fellow researchers about their amazing voyage to the bottom of Lake Superior, where no fishing net has gone before and the amazing discovery they made. It's a legendary study, a great story and it has only just begun.