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By Phil Moy, Wisconsin Sea Grant Institute
Lake Superior reigns as the largest of the Great Lakes in both area (31,700 acres) and volume (2,900 cubic miles) and holds enough water (3 quadrillion gallons) to supply the United States’ daily fresh-water requirements for about 25 years.
But when it comes to sustaining life in its vast, cold waters, Lake Superior juggles a more fragile balance than the more fertile lower Great Lakes. The lake is considered “ultra-oligotrophic” because of the very low concentrations of nutrients and other materials to support life in its waters. Despite that, it supports both recreational and commercial fisheries.
Historically, commercial fishing operations harvested whitefish, lake trout, lake herring and sturgeon. Today, although lake herring are abundant, they are not as popular as they once were with consumers and are more often a holiday purchase.
Methods allowed for commercial catch have shifted in recent years from large-mesh gill nets to pound (pond) nets, and as a result the total commercial harvest has been reduced. From 1992 to 1996, the annual value of the catch remained near or above $300,000; this value has fallen in recent years with reduced price received for the catch. Gill netting is still used by some Native American fishers for both commercial and traditional fishing, but that practice also has been reduced among commercial fishing operations.
Lake Superior supports the only remaining naturally sustaining population of lake trout in the Great Lakes. One subspecies of lake trout, the fatty siscowet, basically thrives only in the deep waters and consistently chilly temperatures of Lake Superior. Lake trout populations in the lower lakes are supported through stocking programs. Lake trout in all of the Great Lakes were devastated by the invasion of the sea lamprey, an eel-shaped parasitic fish that gained access to the upper Great Lakes via the Welland Canal. The canal was constructed in 1829 to allow ships to pass around Niagara Falls.
In addition to the sea lamprey, other prominent invasive species affecting Lake Superior are the zebra mussel, round goby, ruffe, white perch, three-spine stickleback and two species of planktonic crustaceans with long spines. Zebra mussel, round goby and ruffe and the zooplankton came to the Great Lakes via ballast water and are native to Europe. Like lamprey, white perch and three-spine stickleback are Atlantic coast species that likely gained access to the upper Great Lakes via the Welland Canal. These unwanted residents prey upon our native species and compete with them for habitat and forage.
Some nonindigenous species can be welcomed and even are introduced. Rainbow smelt is an accidental introduction from the species native to the Atlantic coast and one fresh-water lake in Maine. The Great Lakes population began after smelt escaped from a lake in Michigan in the 1920s and appeared in Lake Superior in the 1940s. These small, silvery fish congregate along shorelines near creek mouths in the spring to spawn and can provide a tasty reward for dip netters along the Lake Superior shoreline.
Chinook, coho, Atlantic and pink salmon and steelhead trout are among those nonindigenous species intentionally stocked or managed for the multimillion-dollar charter and recreational fishing industry. Northern pike, walleye, lake trout, brown trout and brook trout are native species available for anglers in Lake Superior and its tributaries.
Meanwhile, two other native species are getting special stocking attention. Many governmental and tribal entities are stocking coaster brook trout, a native species almost lost to the lake. Lake sturgeon, which was extirpated from the St. Louis River and the western portion of Lake Superior, have been restocked for the past 20 years. Those first-stocked females may now be mature enough to reproduce the long-lived (up to 100 years) species.
Though recovering in many ways, Lake Superior’s fisheries are still challenged by habitat degradation and chemical pollution that occurred during two centuries of development and more recently the biological pollution - invasive species. We must not take the fisheries of Lake Superior for granted; they are a gift that must be nurtured and cherished.
Phil Moy is with the advisory services of the Wisconsin Sea Grant Institute in Manitowoc.
