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Lake trout, lake whitefish and lake herring are sold commercially, and lake trout are fished for sport.
Commercial fishing began in the 1830s and increased in intensity over the next century. Lake whitefish were heavily fished in the Wisconsin waters in the 1870s and 1880s. Over-fishing had already taken its toll on lake trout, lake whitefish and lake herring populations by 1938, when sea lamprey reached Lake Superior.
"Lake whitefish, the most sought-after species, were more shore-oriented than lake trout," said DNR fish biologist Dennis Pratt. "When whitefish numbers got low, fishermen turned to lake trout. When sea lamprey arrived, they nearly eliminated the depressed lake trout populations. Lake herring sustained the commercial fishery into the 1950s, but by the 1960s, herring numbers were down, too."
The 1960s were a low point for the lake's fishery.
Special effort was put into restoring the lake's top native predator – the prized lake trout. Since the 1960s, management efforts have reduced lake trout mortality by managing lamprey predation and human harvest. Wisconsin created two fish refuges where limited lake trout fishing is allowed: Gull Island Refuge (1976) and Devils Island Refuge (1981). Gull Island Reef is one of the few places where a remnant lake trout spawning population survived the lamprey invasion.
While reducing lake trout mortality, biologists increased fish numbers by stocking fish and eggs. They placed some fertilized eggs inside Astroturf bundles on Devils Island shoal, hoping the fish would return as adults to spawn.
"We are beginning to see the results of that work, as the fish reach spawning age," said DNR fish biologist Steve Schram. These lake trout are slow growing, and can reach a ripe old age.
"We have caught 42-year-old trout," he said, "and we suspect others are even older."
Lake Superior lake trout have recovered sufficiently enough that stocking is no longer necessary in most locations. Lake whitefish and lake herring also rebounded. Two relatively new species originally stocked in Lake Superior by the State of Michigan – coho and chinook salmon – have become naturalized and are reproducing on their own. Coho salmon are the second most commonly caught sport fish in the Wisconsin waters of Lake Superior.
Lake trout, coho salmon and chinook salmon grow faster and larger in Lake Michigan, but they don't reproduce there.
"In Lake Michigan, all the major game species are stocked. With so much natural reproduction here, we have different management challenges," Schram said.
Lake trout have recovered on Lake Superior, but there is a catch. There are two primary strains of lake trout: lean lake trout and siscowet, which can be 70 percent fat by weight. Historically, there were more lean lake trout than siscowet, but we now have more siscowet.
While fat helps fish regulate buoyancy in deep water, people don't want oily fish. Jim Kitchell, a fishery ecologist and Director of the Center for Limnology at the University of Wisconsin-Madison, called this Superior's blessing and curse. "The blessing is that the lake is almost 'full up' with lake trout. The curse is they aren't the kind people want," Kitchell said. "Siscowet are long-lived and grow at half the rate of lean lake trout, so there is a huge mortgage to pay, with the currency being the lake's forage species: smelt, herring and sculpin."
That's a big price to pay in a lake where fish reproduce and grow so slowly.
Nancy Larson is Wisconsin DNR's Lake Superior program coordinator. Karen Plass is a former Lake Superior specialist with the Wisconsin DNR and former executive director of the St. Louis River Citizens Action Committee; she currently works for the University of Minnesota-Duluth.