The Great Lakes, holding nearly one-fifth of the world’s surface freshwater, support a diverse and complex aquatic community. This vast freshwater environment is home to a mixture of native species, intentionally introduced fish, and accidentally established invaders. The fishery within these lakes reflects both the basin’s natural history and the pressures of human activity, including commerce, stocking, and habitat alteration. The variety of fish life provides both a substantial economic resource and a challenge for environmental management agencies in the United States and Canada.
Native Fish Species
The Lake Trout, a large char, historically functioned as the apex predator in the deeper, colder reaches of the lakes. This native species was once abundant and a primary target of early commercial fishing operations, but its population collapsed in the mid-20th century across most of the basin.
The various species of Whitefish and Cisco have long formed the foundation of the commercial fishery. Lake Whitefish remains a highly valued commercial catch, thriving on bottom-dwelling invertebrates. Cisco, or Lake Herring, were once crucial forage fish in the open-water food web, sustaining larger predators like the Lake Trout.
Another iconic native species is the Lake Sturgeon, the oldest and largest fish in the Great Lakes, characterized by its bony plates instead of scales. These bottom-feeding fish are extremely slow to mature, with females taking 20 to 25 years before they can spawn. They can live for over a century. The Lake Sturgeon’s long lifespan and delayed reproduction make its recovery from historic overfishing and habitat destruction a slow and difficult process.
Established Non-Native Sport and Commercial Fish
Many fish that draw recreational anglers to the Great Lakes are not native but were intentionally introduced. The most prominent examples are the Pacific Salmon species, Chinook and Coho Salmon, which were first stocked extensively in the 1960s. This stocking program was primarily designed to establish a lucrative sport fishery and control the burgeoning population of invasive Alewife.
Chinook Salmon and Coho Salmon have adapted well to the deep, cold waters, providing a world-renowned recreational fishery. Chinook Salmon were favored for their fast growth, high predation rate on Alewife, and the exciting fight they offer anglers.
Other intentionally introduced species that now support significant recreational fishing include Rainbow Trout, often called Steelhead in its lake-migrating form, and Brown Trout. Steelhead are stocked extensively. Unlike Pacific Salmon, which typically die after spawning, Steelhead can survive to spawn multiple times, returning to the tributaries year after year. The sustained presence of these species remains dependent on continuous, large-scale stocking programs.
Invasive Species Disrupting the Ecosystem
The Great Lakes ecosystem faces constant pressure from non-native species that were introduced accidentally. The Sea Lamprey, an eel-like parasitic fish, is one of the most historically destructive invaders, having entered the upper lakes through shipping canals. This predator attaches to fish with its sucking disk mouth and feeds on blood and body fluids.
The Round Goby is another pervasive accidental invader, arriving via the ballast water of transoceanic ships. Round Gobies aggressively compete with native species for food and habitat, and they actively prey on the eggs and fry of native fish. Although the goby is now a food source for some native predators, it can also pass on contaminants like botulism to the larger fish and birds that consume it.
A major concern for the basin is the potential establishment of Asian Carp species, Bighead and Silver Carp, currently found in the Mississippi River system. These species are voracious filter feeders that consume massive volumes of plankton, threatening to strip the base of the food web. Their establishment would likely disrupt the entire aquatic community by outcompeting many native and stocked fish for microscopic organisms.