Lake Michigan, the third-largest Great Lake and fifth-largest lake globally by surface area, is a vast freshwater expanse entirely within the United States. Spanning approximately 22,400 square miles (58,000 square kilometers), its diverse underwater landscapes and shorelines support a rich aquatic ecosystem. Historically home to numerous fish species, the lake’s ecosystem has faced various challenges.
Native Fish Populations
Lake Michigan was once home to approximately 150 native fish species, forming the foundation of its aquatic communities. These indigenous inhabitants include the Lake Trout, Lake Whitefish, Yellow Perch, and Lake Sturgeon. These species have adapted to the lake’s specific conditions, thriving in various habitats across its depths and nearshore areas.
Lake Trout (Salvelinus namaycush) are deep-water fish, preferring colder, deeper regions. Their populations declined significantly by the 1950s due to overfishing and invasive species. Lake Whitefish (Coregonus clupeaformis) are another native species, found in cold waters and often feeding along the bottom, particularly in the northern parts of the lake.
Yellow Perch (Perca flavescens), a schooling species, primarily inhabits nearshore areas, usually in depths less than 30 feet. Their numbers have decreased notably since the 1990s. The Lake Sturgeon (Acipenser fulvescens), a large and long-lived fish, resides nearshore in depths between 15 and 60 feet. These bottom feeders consume small animals like snails, crustaceans, and aquatic insects.
Introduced Species and Their Impact
Non-native fish species have significantly altered Lake Michigan’s ecosystem, often arriving unintentionally through pathways like ballast water. The Sea Lamprey (Petromyzon marinus) entered the Great Lakes via the Welland Canal, observed in Lake Michigan by 1936. This parasitic animal attaches to fish with a suction-cup mouth, feeding on their blood and fluids, often killing the host. Before control measures, sea lampreys killed over 100 million pounds of Great Lakes fish annually, severely impacting native populations like lake trout.
The Alewife (Alosa pseudoharengus), an Atlantic species, also invaded Lake Michigan and proliferated due to diminished native predator populations. By 1965, alewives comprised 90% of the lake’s fish biomass, leading to massive die-offs that littered shorelines in the 1960s. Alewives negatively affect native species by consuming their early life stages and competing for zooplankton.
Pacific Salmon, including Chinook and Coho Salmon, were intentionally introduced in the 1960s to control the burgeoning alewife population and establish a sport fishery. These salmon now primarily feed on alewives, contributing to their population control. The Round Goby (Neogobius melanostomus), introduced around 1990 via ballast water, is native to the Black and Caspian Seas. Round gobies consume zebra and quagga mussels, but also compete with native fish for food and prey on their eggs.
Ecological Contributions of Lake Michigan Fish
Fish play a fundamental role in the Lake Michigan ecosystem, serving as important links in the food web and providing insights into its overall health. Different species occupy various positions, from primary consumers to apex predators. Phytoplankton are consumed by zooplankton, which then become food for smaller foraging fish like sculpin and perch.
These smaller fish serve as prey for larger predatory species, including walleye, trout, and salmon. Native species such as ciscoes, sculpins, and shiners sustain many of the lake’s top predators, including lake trout and walleye. The migratory patterns of some fish, such as salmon and trout, also contribute to nutrient cycling within the lake’s waters.
The presence or absence of certain fish species can indicate environmental conditions. For example, smallmouth bass are sensitive to pollution, so a healthy population suggests a clean environment. However, invasive mussels like zebra and quagga mussels have reduced phytoplankton and zooplankton populations. This reduction in foundational food sources directly impacts prey fish abundance, affecting the entire food web.
Managing Fish for the Future
Effective management of Lake Michigan’s fish populations requires a collaborative approach involving multiple agencies and stakeholders. Stocking programs, where agencies release salmon and trout into the lake, sustain recreational fisheries and maintain a balance between predator and prey populations. Lake trout rehabilitation relies on continued stocking to support their resurgence.
Control of invasive species is another component of management. Efforts focus on species like the sea lamprey, through methods such as applying lampricides in their spawning habitats. These interventions have successfully reduced sea lamprey populations by more than 90% from their peak numbers.
Habitat restoration projects also improve conditions for native fish. These initiatives include restoring rocky reefs for spawning grounds and removing barriers to fish passage in tributary streams. This ensures fish have access to breeding and nursery areas. Fishing regulations, including daily bag limits and size restrictions, also manage the harvest of various species. These regulations promote sustainable fish populations for both recreational and commercial fishing.