Lake Michigan, a vast freshwater body spanning over 22,000 square miles, supports a rich diversity of fish species. Understanding these inhabitants, both native and introduced, provides insight into the ecological changes and ongoing management efforts within this significant Great Lake. Its varied habitats, from shallow nearshore areas to cold, deep waters, contribute to the array of fish found within its expanse.
Lake Michigan’s Original Fish Inhabitants
Lake Michigan has historically been home to native fish species that formed the basis of its aquatic food web and supported early fisheries. Lake Trout, once the top native predator, were abundant in the lake’s cold, deep waters. Their populations faced severe declines due to overfishing and invasive species, leading to near extinction by 1956, prompting significant rehabilitation programs.
Another important native species is the Lake Whitefish, a cool-water fish highly valued for commercial fishing. These fish primarily feed on bottom-dwelling invertebrates like Diporeia, which are small, shrimp-like organisms. Lake Whitefish often school in deeper waters as temperatures rise.
Cisco, also known as Lake Herring, were once a crucial prey fish, sustaining larger predatory species. Several cisco species faced significant declines in the early 20th century. Yellow Perch remain a popular native species, appreciated by anglers for both sport and food, inhabiting both shallow and deep parts of the lake. They serve as an important prey source for larger fish.
Walleye, another popular native sport fish, can be found throughout Lake Michigan. Some populations reproduce naturally in the lake’s tributaries. These fish are highly prized for their flesh. While their numbers in the main lake are often supplemented by stockings into connecting rivers, they contribute to the lake’s diverse native fish community.
The Impact of New Fish Species in the Lake
New fish species have been introduced into Lake Michigan, profoundly altering its ecosystem. Many Pacific salmon and trout species were intentionally stocked starting in the 1960s to create a sport fishery and help control burgeoning populations of invasive Alewives. Chinook Salmon, known as “King Salmon,” are a highly sought-after game fish. Coho Salmon, also called “Silver Salmon,” are another popular species for anglers.
Rainbow Trout, often referred to as Steelhead when they migrate to the lake from rivers, and Brown Trout are also regularly stocked. These introduced salmonids have adapted to the lake’s environment, supporting a significant recreational fishing industry. Stocking levels for these species are carefully managed by state agencies to balance the predator-prey relationship within the lake.
Beyond intentional introductions, several species have arrived unintentionally, becoming invasive and causing widespread ecological changes. The Sea Lamprey, a parasitic fish native to the Atlantic Ocean, entered the Great Lakes through canals in the early 20th century. With a suction-cup mouth, they attach to native fish, consuming their blood and bodily fluids, often leading to the host fish’s death. This predation severely impacted native fish populations, including Lake Trout, before extensive control efforts reduced lamprey numbers by over 90 percent.
Alewives, a small, silvery fish from the Atlantic, also invaded the Great Lakes through canals, becoming widespread by the 1960s. Their population explosions led to massive die-offs, and they negatively impacted native fish by competing for food and preying on the early life stages of species like Yellow Perch and Lake Trout. While they became a primary food source for stocked salmon, their decline in recent years has raised concerns for the salmon fishery.
The Round Goby, an aggressive bottom-dwelling fish from Eurasia, arrived in the Great Lakes via ship ballast water in the 1990s. They reproduce rapidly, consuming food native fish need and preying on the eggs of sport fish like Lake Trout, Walleye, and Smallmouth Bass. This species also competes with native bottom-dwelling fish.
Understanding Lake Michigan’s Fish Ecosystem
The health and diversity of Lake Michigan’s fish populations depend on environmental conditions and ongoing management. Habitat quality, encompassing clean water, suitable spawning grounds, and protective nursery areas, is fundamental for fish survival and reproduction. Agencies work to protect and restore critical habitats.
The lake’s food web dynamics have been significantly altered by invasive species, particularly Zebra and Quagga mussels. These mussels are highly efficient filter feeders, consuming vast amounts of phytoplankton. This reduction in primary productivity impacts zooplankton and Diporeia, which are essential food sources for many fish species, including the commercially important Lake Whitefish. The decline in these foundational food sources can lead to reduced growth and survival for various fish populations.
Human management and conservation efforts play a substantial role in maintaining Lake Michigan’s fishery. State and federal agencies collaborate on stocking programs for various salmon and trout species, aiming to balance predator and prey populations and ensure sustainable fishing opportunities.
Fishing regulations, such as catch limits and seasons, are implemented to prevent overfishing and allow fish stocks to regenerate. Beyond stocking and regulations, extensive efforts are directed towards controlling invasive species, like the Sea Lamprey. Habitat restoration projects and water quality monitoring also contribute to the overall health and sustainability of Lake Michigan’s fish ecosystem.