Lake Superior, the largest freshwater lake by surface area globally, is a vast ecosystem. Its immense size, depth, and cold, nutrient-poor waters create a distinctive environment. These characteristics shape the aquatic life it sustains, supporting diverse fish species adapted to its conditions.
Native Fish Species of Lake Superior
Lake Superior is home to several prominent native fish species, each playing a specific role in the lake’s ecosystem. The Lake Trout (Salvelinus namaycush) is a top predator, with distinct forms like the “lean” lake trout in shallower waters and the “siscowet” in deeper areas. These fish can grow quite large, with siscowets becoming very fat. Lake Whitefish (Coregonus clupeaformis) are abundant, characterized by a silvery appearance and a snout that overhangs a short lower jaw, allowing them to feed on the lakebed. They are a significant commercial fish.
Cisco (Coregonus artedi), sometimes referred to as lake herring, are a crucial prey fish, primarily consuming zooplankton and aquatic insect larvae. They mature at 9-12 inches and spawn in shallow waters as temperatures drop in late fall or early winter. Burbot (Lota lota), a freshwater cod relative, are cold-water dwellers found in the deepest parts of Lake Superior. These elongated, mottled fish are nocturnal predators, feeding on other fish, fish eggs, and crustaceans.
Several sculpin species inhabit Lake Superior, including the slimy sculpin (Cottus cognatus), spoonhead sculpin (Cottus ricei), and deepwater sculpin (Myoxocephalus thompsoni). These bottom-dwelling fish are generally small, typically reaching 3-3.6 inches. They primarily consume burrowing amphipods and opossum shrimp, and deepwater sculpins are a significant prey item for lake trout.
Introduced and Invasive Fish Species
Lake Superior’s ecosystem has been altered by various non-native fish species, some introduced intentionally and others accidentally. Pacific Salmon species, such as Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) salmon, and Rainbow Trout (Oncorhynchus mykiss) were introduced for sport fishing. These species have established populations and contribute to the lake’s diverse fishery.
Invasive species pose challenges, notably the Sea Lamprey (Petromyzon marinus) and the Round Goby (Neogobius melanostomus). Sea Lampreys entered the Great Lakes through shipping canals, reaching Lake Superior by 1938. These parasitic fish attach to native fish, feeding on blood and body fluids, with a single lamprey capable of destroying 40 pounds of fish during its feeding period. The Round Goby, originating from Eurasia, was first detected in Lake Superior in 1995, likely introduced via ship ballast water. This aggressive bottom-dweller competes with native species like sculpins for food and spawning sites, and can consume fish eggs.
Environmental Influences on Fish Populations
The unique characteristics of Lake Superior significantly influence its fish populations. As the largest and deepest of the Great Lakes, it maintains exceptionally cold water temperatures throughout the year. This cold environment favors species adapted to cooler conditions, such as trout, whitefish, and sculpins. The lake is oligotrophic, meaning it has low nutrient levels, which results in lower overall biological productivity.
Despite low nutrient levels, Lake Superior’s vast volume and high oxygen content support a robust cold-water fishery. This combination of cold, deep, and oxygen-rich waters provides suitable habitat for cold-water species. The physical structure of the lake, with its deep offshore areas and shallower nearshore zones, creates diverse microhabitats that different fish species utilize for feeding, spawning, and shelter.
Conservation and Management Efforts
Protecting and managing Lake Superior’s fish populations involves collaborative efforts among various agencies. Stocking programs have been implemented, such as the historical stocking of Lake Trout for rehabilitation, though this has been phased out in some areas due to successful natural reproduction. Chinook salmon stocking continues in some regions to support recreational fishing.
Regulations on fishing, including catch limits and seasons, are in place to manage fish harvest and ensure sustainable populations. A significant focus of management has been on controlling invasive species. The Sea Lamprey control program uses lampricides to target larval lampreys in tributaries and employs barriers and traps to prevent adult migration. These efforts have reduced sea lamprey populations. Habitat restoration initiatives contribute to conservation, aiming to improve conditions for native fish species and support the overall health of the lake’s aquatic ecosystem.