Lake Superior, the world’s largest freshwater lake by surface area, provides a unique environment for its animal inhabitants. Its immense depth, cold temperatures, and low nutrient levels (oligotrophy) shape the life that thrives within its waters and along its shores. These characteristics create a specialized ecosystem supporting diverse species. Its vastness and connection to terrestrial habitats contribute to the richness of its animal communities.
Fish Species
Lake Superior’s cold, oxygen-rich waters provide habitat for 88 fish species, 34 of which are native. Lake Trout (Salvelinus namaycush) are apex predators thriving in deep, cold waters, with different forms adapted to specific niches. These include lean lake trout, which prefer depths shallower than 160 feet and primarily feed on smaller fish, and siscowet lake trout, which are fattier and inhabit extremely cold, deep waters, sometimes exceeding 1,330 feet.
Lake Whitefish (Coregonus clupeaformis) are bottom-dwelling fish, feeding on insects, freshwater shrimp, and other small organisms near the lakebed. They are recognizable by their small heads and silvery to white coloration with an olive to pale greenish-brown back. Ciscoes (Coregonus artedi), also known as lake herring, are schooling fish that primarily consume microscopic zooplankton, though they also eat aquatic insect larvae and other bottom-dwelling invertebrates. These fish are sensitive to warm water and low oxygen levels, making Lake Superior a stronghold for their populations compared to other Great Lakes.
Lake Sturgeon (Acipenser fulvescens) are the largest and oldest native fish in the Great Lakes, living over 100 years and reaching lengths of six feet or more. These bottom feeders use their sensitive barbels to locate prey like snails, crayfish, and insect larvae. Introduced species, such as Rainbow Smelt and various salmon species like Chinook and Coho, have also established populations, contributing to the lake’s fish diversity.
However, invasive species pose ongoing challenges to the lake’s native fish populations. The Sea Lamprey, a parasitic fish that entered the Great Lakes through shipping canals, has impacted native fish like Lake Trout, Lake Whitefish, and Cisco by feeding on their blood. Control efforts have reduced lamprey numbers, but their presence continues to affect the ecosystem. The Round Goby competes with native bottom-dwelling fish for food and habitat and preys on fish eggs, including those of Lake Trout and Lake Sturgeon.
Avian Inhabitants
Lake Superior and its surrounding areas provide essential resources for diverse bird species, serving as habitat for feeding, breeding, and migratory stopovers. Waterfowl are prominent, with Common Loons (Gavia immer) frequently seen on the lake. While loons do not typically nest directly on Lake Superior, they utilize its open waters for fishing and are found there during spring, fall, and summer migration. Their diet includes various fish, crustaceans, and aquatic insects, abundant in the lake.
Various duck species also frequent the lake, including mallards, buffleheads, common goldeneyes, hooded mergansers, and common mergansers. During colder months, Lake Superior hosts species that typically nest further north, such as Harlequin Ducks, Long-tailed Ducks, White-winged Scoters, Black Scoters, and Surf Scoters. These birds often forage in the lake’s nearshore waters; some, like Long-tailed Ducks, can dive to depths of 200 feet for food.
The shoreline and adjacent forests are also home to various gulls and raptors. Herring Gulls (Larus smithsonianus) are among the most common gulls on Lake Superior, present year-round and often seen scavenging or feeding on fish. Other gull species, such as Ring-billed Gulls, also frequent the area, with some migrating south for winter.
Raptors, including Bald Eagles (Haliaeetus leucocephalus), are commonly observed soaring over the lake or perched in tall trees along the shore. Bald Eagles primarily feed on fish, but will also scavenge. The Lake Superior region is also a corridor for raptor migration in the fall, with thousands of hawks, eagles, and falcons, including Broad-winged Hawks, Sharp-shinned Hawks, and Golden Eagles, funneling along the lakeshore. Shorebirds, such as sandpipers and plovers, also utilize the Lake Superior shoreline during their spring and fall migrations.
Mammals of the Lake and Shore
Lake Superior’s diverse ecosystem extends beyond its waters to the surrounding land, supporting various mammals. Aquatic and semi-aquatic mammals include beavers (Castor canadensis), river otters (Lontra canadensis), and muskrats (Ondatra zibethicus) found in the lake’s tributaries and along its marshy edges. Beavers, known as ecosystem engineers, build dams and lodges that alter local habitats, creating ponds and wetlands. River otters, agile swimmers and playful members of the weasel family, hunt fish and other small aquatic organisms, making dens along the shoreline with both underwater and above-ground entrances. Muskrats, a large rodent, build dome-shaped lodges from vegetation and burrow into banks, feeding primarily on aquatic plants.
Terrestrial mammals also frequent the Lake Superior shoreline. Moose (Alces alces), the largest member of the deer family, are found in the boreal forests of the Lake Superior region, particularly on Isle Royale, where they interact with wolves. Black bears (Ursus americanus) are common in the heavily forested areas surrounding the lake, including the Superior National Forest. These omnivores forage for berries, insects, and other food sources, sometimes venturing near human settlements.
White-tailed deer (Odocoileus virginianus) are abundant throughout the forested areas, often seen along roadsides and near the shoreline, especially in winter when the lake’s warmth attracts them. Wolves (Canis lupus) are also present, notably on Isle Royale, where they regulate the moose population. Other mammals observed in the region include red foxes, coyotes, and porcupines.
Smaller Aquatic Organisms
Lake Superior’s cold, clear waters also support smaller aquatic organisms important to the food web. Zooplankton, microscopic animals that drift, are a primary food source for many fish, especially in their early life stages. The zooplankton community in Lake Superior is characterized by species adapted to oligotrophic, coldwater conditions, such as calanoid copepods. Opossum shrimp (Mysis relicta) are another important zooplankton component, migrating vertically and serving as a prey item for various fish species, including rainbow smelt, bloater, and lake whitefish.
The lakebed and nearshore areas host diverse benthic invertebrates. These include insect larvae, such as chironomids (midge flies) and mayfly nymphs, which feed on detritus and algae. Mayfly nymphs are often found in warmer, shallower bays. Amphipods, like Diporeia spp., are dominant macroinvertebrates in Lake Superior, inhabiting depths between 30 and 125 meters and serving as a food source for deepwater sculpin.
Crayfish are also present in Lake Superior, with the native Virile Crayfish. However, the invasive Rusty Crayfish poses a threat by outcompeting native species and preying on fish eggs. Freshwater mussels are another group of invertebrates, with both native and invasive species like zebra and quagga mussels found in the lake. While Lake Superior’s cold temperatures and low calcium concentrations make it less hospitable for these invasive mussels than other Great Lakes, they have established populations in some areas, such as harbors and around the Apostle Islands.
Amphibians, though less directly aquatic than fish or invertebrates, are found in wetlands and near the lake’s edges. Species like the Wood Frog (Lithobates sylvaticus), American Toad, and various salamanders utilize ponds and moist woodlands for breeding and habitat. These smaller organisms collectively support the aquatic ecosystem of Lake Superior, cycling nutrients and providing sustenance.