Animals

Top Five Great Lakes Invaders

Sea Lampreys
Sea lampreys, a primitive jawless fish native to the Atlantic Ocean, began invading the Great Lakes in the 1920s. For part of its life cycle, the sea lamprey feeds on the blood and tissue of larger fishes, consuming up to 40 pounds of fish. Sea lampreys contributed to the population collapses of several large Great Lakes fishes, including lake trout, turbot and lake whitefish. Before sea lampreys invaded Lake Superior, the lake trout harvest averaged 4.5 million pounds. By 1960, it was less than 500,000 pounds.

Zebra and Quagga Mussels
While zebra mussels were a large concern over the past decade, their threat is being overshadowed by the more recently introduced quagga mussels. Quagga mussels can live in deeper, colder water than their zebra mussel cousins, enabling the quagga to capitalize on a previously uninhabited niche. Both of these mussels filter-feed up to a liter of water a day, removing large amounts of phytoplankton and decreasing the food supply for other species. A single female can produce more than a million eggs in a spawning season, creating an abundance of mussels to clog water intake structures, requiring costly upkeep and repairs.

Round Goby
The round goby is a bottom-dwelling fish less than 7 inches long, introduced in 1990 through contaminated ballast waters of transoceanic ships. A voracious feeder that can forage in total darkness, the goby’s effective sensory system detects water movement better than native fishes’, giving it a food-foraging advantage. Anglers have reported areas where round gobies appear to be the only fish present.

Spiny Water Flea
The spiny water flea is a not an insect but a crustacean with a sharp barbed tail spine that makes up 70 percent of its inch-long body and is used for protection. With few predators, populations of the spiny water flea are booming, causing populations of its food, plankton, to decline. This means a shortage of food for other species that also eat plankton, like small fishes and zooplankton. A rapid reproducer, female spiny water fleas can produce up to 10 offspring every two weeks in the summer months. In lakes dominated by the spiny water flea, anglers often find cottony clumps of the species entangled on their fishing lines that are so massive that their lines must be cut.

Asian Carp
A potential Great Lakes invader, Asian carp include four species: black carp, grass carp, bighead carp and silver carp. These large fishes (weighing up to 110 pounds) were imported into the United States for use in aquaculture in southern states. Flooding allowed bighead and silver carp to escape fish farms and enter the Mississippi River, where they quickly swam upstream into the Illinois River. If Asian carp enter the Great Lakes, via the Chicago Sanitary and Ship Canal, they are expected to become a dominant species due to a lack of predators, high reproductive rates and their ability to crowd out other fishes. Asian carp consume huge amounts of the same food eaten by native fishes, aggressively outcompeting them and eventually displacing them altogether. Silver carp periodically leap out of the water when startled, injuring boaters, skiers and anyone else in their path. Asian carp spotted just 50 miles from Lake Michigan are being prevented from entering the Great Lakes by an electric barrier in the waters of the Chicago Sanitary and Ship Canal. The barrier is only a temporary solution that requires ongoing support.

Click here to see what you can do.