Are There Sharks in the Great Lakes? - American Oceans (2024)

The Great Lakes, known for their vast freshwater ecosystems and numerous aquatic species, have sparked curiosity amongst people regarding the possibility of shark inhabitants. While it might seem an unlikely habitat for these predators, some might wonder if a species like bull sharks, capable of surviving in both saltwater and freshwater, could find their way into these vast lakes.

Historically, there have been rare sightings and claims of sharks in the Great Lakes, fueling speculation and even leading to some hoaxes. However, no concrete evidence has been found to support the presence of sharks in these freshwater lakes. Bull sharks, known for their ability to adapt to freshwater habitats, have been found in other locations, such as Lake Nicaragua, but not in the Great Lakes.

Scientists and researchers have extensively studied the Great Lakes’ ecosystems and the various species inhabiting these waters. Despite the occasional rumors or alleged sightings, their research has not produced any confirmation that sharks reside in the Great Lakes. The vastly different environment compared to shark habitats, along with the lack of concrete evidence, reinforces the idea that these apex predators are not present in these freshwater lakes.

Shark Presence in the Great Lakes

Throughout history, there have been occasional reports of shark sightings in the Great Lakes, particularly in Lake Michigan, Lake Superior, Lake Huron, Lake Ontario, and Lake Erie. However, most of these reports have turned out to be hoaxes or misidentifications of other aquatic animals. For example, a famous incident occurred in 1955 in Alton, Illinois, where locals claimed to have seen a shark in the Mississippi River, which subsequently turned out to be a large catfish. Another more recent example is a viral 2017 Instagram post from Lake Ontario, claiming to show a bull shark swimming in the lake, that was later debunked.

Biological Feasibility of Sharks in Freshwater Environments

In terms of biological feasibility, there are very few shark species capable of surviving in freshwater environments. The bull shark (Carcharhinus leucas) is one of the rare examples of a shark species that can tolerate fresh water, being found in some rivers and freshwater lakes around the world. They possess a unique physiological structure, including special gills and a kidney system that allows them to maintain their buoyancy and osmoregulate in freshwater.

However, the Great Lakes ecosystem is not a suitable habitat for bull sharks or any other shark species, due to several factors:

• Water temperature: Most shark species, including bull sharks, prefer warmer waters. The Great Lakes have a relatively cold water temperature year-round, which is not conducive to shark survival.

• Accessibility: Sharks would have to swim up the Mississippi River or other connected waterways to reach the Great Lakes, which is a long and challenging journey. There are also man-made obstacles such as locks and dams that can impede their passage.

• Availability of prey: The Great Lakes ecosystem is significantly different from the sharks’ natural habitats, and the types of prey available may not be sufficient or suitable for sustaining a shark population.

Factors Limiting Shark Survival in the Great Lakes

The primary factor preventing sharks from inhabiting the Great Lakes is the extensive geographical and man-made barriers. The Laurentian Great Lakes are a collection of freshwater lakes located primarily in the United States and extending into Canada, connected via the Mississippi River. Sharks are predominantly saltwater creatures and would struggle to adapt to freshwater ecosystems. Additionally, even if a shark managed to swim up the Mississippi River, it would still have to navigate through the nearly impassable system of locks and dams that link the lakes together. Furthermore, an electric barrier has been installed in the Illinois River (near St. Louis and Minnesota) to discourage the spread of invasive species, such as Asian carp, effectively hindering any potential shark migration.

Environmental Conditions and Ecosystem Dynamics

The Great Lakes present a unique set of environmental conditions and ecosystem dynamics that would prove challenging for shark survival. While some sharks, like the bull shark, can tolerate freshwater and brackish environments, the majority require saltwater for survival. The lakes are generally colder in surface temperature, especially in the winter months, which is not optimal for most shark species. Additionally, among all the lakes, Lake Erie is the shallowest, making it the least conducive for shark survival, while other lakes like Ontario, Michigan, and Huron are deeper but still lack conditions necessary for shark adaptation.

Predatory Relationships and Available Prey

Another limiting factor for sharks in the Great Lakes is the composition of available prey and local predators. The Great Lakes Fishery Commission manages fishery populations, focusing on native species such as bass, northern pike, trout, perch, muskellunge, salmon, and lake sturgeon. The presence of predatory fish, such as the muskellunge, adds an element of competition for available food sources. Sharks would also have to compete for prey with introduced species like the invasive Asian carp. Although the Great Lakes contain plenty of fish, the absence of warm-water estuaries and coastal habitats generally preferred by sharks exacerbates these challenges in finding appropriate food sources.