Sea lamprey and dreissenid mussels and round gobies, oh my! Invasive species have been in the Great Lakes since early alterations to the system in the late 1800s. These canal systems were designed to circumvent rapids and Niagara Falls to more easily facilitate trade. An unintended consequence, with long-reaching impacts, has been the introduction and spread of invasive species throughout the Great Lakes. Some of the most visible and well known invasives include sea lamprey, zebra and quagga mussels and round gobies, which have all significantly altered the food web dynamics of the Great Lakes.
Sea lamprey (Petromyzon marinus) were first discovered in Lake Erie in 1921, Lake Michigan in 1936, Lake Huron in 1937, and Lake Superior years later. An anadromous fish (live in salt water, spawn in freshwater), sea lamprey easily adapted to the freshwater lakes and quickly brought the Whitefish and Lake Trout fisheries to their knees. These jawless, parasitic fish spawn in many of the Great Lakes’ tributaries and present environmental managers with many difficulties. In their larval form, these fish burrow into the stream bottom and their maturation can take up to 18 years. Once mature, these fish will swim into the lakes, begin feeding and return to the streams to spawn in a year. A single female can release hundreds of thousands of eggs. Management efforts have included a sterile male release program which target male sea lamprey, sterilize them and then released them into streams. Lampricides have also been utilized to eradicate sea lamprey larva in streams. Lampricide is an effective, targeted chemical that kills lamprey larva without killing other, more evolved fish species. One major drawback is that lampricides also kill native lamprey larva. A recent development is the use of pheromones to manipulate sea lamprey behavior. As pre-historic, nocturnal fish, sea lamprey rely primarily on their olifactory sense when deciding on spawning sites. Dr. Michael Wagner of MSU has been studying the use of pheromones as a tool to help managers to more effectively utilize lampricides. By “directing” sea lamprey into streams through their sense of smell, managers will be able to kill more lamprey larva with a single dose of lampricide, ultimately making the management of these invaders cheaper and more effective.
Zebra and Quagga mussels (Dreissena polymorpha and Dreissena rostriformis) are a well known invader from the Caspian Sea region, that have altered the Great Lakes ecosystem by removing plankton from the water column, leading to significantly clearer water and algae blooms. Dreissenid mussels have long been seen as an unmanageable invader because their larval form is planktonic, and the management of a microscopic organism in a body of water the size and volume of the Great Lakes is all but impossible. Some research was done regarding substrate preferences to see if the mussels were less likely to attach to a specific material but nothing conclusive was revealed. Recently a bacteria that kills the mussels has been discovered. While that alone is exciting, the fact that this bacteria does not negatively impact other species makes this bacteria a viable management tool.
The round goby (Neogobius melanostomus), another invader from the Caspian Sea region was first discovered in Lake Michigan in 1994. Since then, this invasive forage fish has driven the native forage fish further off-shore, into less than ideal habitat. In addition, round gobies aggressively feed on native fish eggs and defend their habitat. Some research has found that there is a piscicide that when released near the bottom of a lake, round gobies are killed, leaving other native species unharmed. Recent research has also found that pheromones can be used to more effectively trap round gobies.
While these invasive species have dramatically altered the Great Lakes in irreparable ways, recent legislation has closed loopholes so that in-coming cargo vessels can no longer be exempt from cleaning their ballast tanks. The closure of these loopholes means that fewer invasive species will be introduced in the future, which will allow the Great Lakes to begin to recover and repair from decades of stress. While the previous invaders are unlikely to be eradicated, the Lakes will find a new equilibrium. Environmental managers have the responsibility to bring invasive species populations to a manageable number so that our native species can recover.
*Pandora’s Locks by Jeff Alexander was used as a general resource.*