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Stout Trout Eyed for Market

Siscowet lake trout. Photo by Jeff Gunderson.

"Lake Superior is a siscowet lake," said Mark Ebener, fishery assessment biologist for the Chippewa Ottawa Resource Authority. Ebener delivered the comment on July 28 at Exploring the Potential for a Siscowet Lake Trout Fishery, a workshop held in response to an interest in commercially harvesting siscowet to produce fish oil supplements and fishmeal. Michigan Sea Grant staff led the workshop in Baraga, Mich., with cosponsors from the Minnesota and Wisconsin Sea Grant programs, the Great Lakes Indian Fish and Wildlife Commission, the Keweenaw Bay Indian Community, and Michigan State University Extension.

Commercial and tribal fishermen, resources managers, and researchers attended. The purpose of the workshop was to review siscowet biology, population estimates, potential sustainable harvest, and to assess the economic feasibility of harvesting them.

Aside from being impressively numerous in Lake Superior, siscowet lake trout have attracted attention for their fatty acids. Siscowet lake trout (also called fats) are the fattiest and most abundant of the three lake trout types still found in Lake Superior. Information presented by Jim Bence, professor and co-director of the Quantitative Fisheries Center at Michigan State University, indicates that there are probably more than 20 siscowets for every lean lake trout in Michiganís waters of Lake Superior.

Most people are more familiar with lean lake trout, which they may catch, purchase at the grocery story, or order from restaurant menus. Because of their high fat content, siscowets are not highly regarded as table fare and because of their deepwater habitat they are not as accessible to sport anglers as lean lake trout. "Fats" primarily live where water depths are greater than 250 feet (76 meters); since 77 percent of Lake Superior is deeper than 250 feet, siscowets have plenty of room to occupy. This is why Lake Superior could be considered a "siscowet lake."

Because the fatty siscowets are not particularly edible, sport anglers are generally not interested in catching them. Experts don't foresee adamant objection to a sustainable commercial fishery for siscowets as long as it doesnít impact the rest of the Lake Superior fish community. Many of the presentations at the workshop addressed concerns about sustainability and food web interactions.

Bence took a modeling approach to estimate siscowet biomass and harvest numbers that could be sustainable. Using lean lake trout catch-per-effort data, lean lake trout abundance estimates, and the ratio of leans to siscowets, he suggested that in Michigan waters alone there might be 170 to 600 million pounds (77,100 to 272,155 metric tons) of siscowets. At a modest harvest rate, commercial fishermen might be able to annually harvest 4 to 15 million pounds (1,815 - 6,800 metric tons). Add Minnesota, Wisconsin, and Ontario waters to the Michigan calculations and youíre talking real siscowet poundage.

Bence cautioned workshop participants about the assumptions and uncertainties that might skew his estimates, but thought there were likely enough siscowets to support a commercial fishery. Another estimate of siscowet biomass for the entire lake by Dan Yule, US Geological Survey, Lake Superior Biological Station Ashland, Wisc., was significantly lower. Yule estimated about 47 million pounds (21,320 metric tons), which could produce an annual harvest of around 1.5 million pounds (680 metric tons) using Benceís moderate harvest rate.

If we caught them, what would we do with them? Prior to the workshop, Subramaniam Sathivel, assistant professor of food engineering at Louisiana State University Agriculture Center and a national expert on designing operations for food processing, received a curious package from Ron Kinnunen, extension educator with Michigan Sea Grant. It contained small, medium, and large siscowets. Sathivel examined fat and protein content of their heads, viscera, skin, and fillets.

At the workshop, Sathivel reported that siscowets provide higher lipid yields than most other marine or freshwater fish species. His estimates of total fat content (wet weight), however, were lower than expected by many of the attendees. He found that medium and large siscowets contained 11-12 percent fat while small ones had 7 percent fat. A similar analysis conducted by Minnesota Sea Grant two decades ago (Wang et al., 1990) found siscowet muscle contained 26 percent fat. Another analysis (Eschmeyer and Phillips, 1965) found siscowets had from 21-48 percent fat (wet weight). This discrepancy remains a mystery.

Sathivel said siscowets also produce high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two types of omega-3 fatty acids that benefit human health. He also estimated that about 17 percent of the weight of a harvested siscowet could be made into fish protein. Insoluble fish protein is suitable for animal consumption while soluble protein can be consumed by humans. Sathivel concluded that commercially harvested siscowet lake trout could be rendered into high quality fish oil and fishmeal.

There are fish and there is a market, but would a commercial fishery be economically worthwhile, even if it was sustainable and did not cause detrimental ripples through the food web? An analysis to determine if it would be economically viable for commercial fishermen to harvest siscowets and for a processor to build a facility needs to happen next. If the economic outlook is promising, it will be up to management agencies and commercial and tribal fishermen to work out the details of a commercial harvest. Lake Superior may be a "siscowet lake," but it could be awhile before the fish oils generated from a commercial siscowet fishery find their way through a processing plant and onto store shelves.

Citations:

JR223. Wang, Y.J., L.A. Miller, M. Perren, and P.B. Addis. 1990. Omega-3 fatty acids in Lake Superior fish. J. Food Sci. 55:71.

Eschmeyer, P. H. and A. M. Phillips Jr., 1965. Fat content of the flesh of siscowets and lake trout from Lake Superior. Trans. Am. Fish. Soc. 94(1): 62-74


By Jeff Gunderson
September 2009

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