Since they were first found in the St. Clair River in 1990, round gobies (Neogobius melanstomus) have spread throughout the Great Lakes and disrupted what is already a fragile ecosystem. While gobies are not the only invasive species that threaten the Great Lakes – others include zebra mussels, Asian carp and double-crested cormorants, just to name a few – gobies are voracious feeders and reproduce with alarming speed, making them some of the most potentially harmful.
Identification
Round gobies can reach 10 inches in length, though individuals between 3 and 6 inches are far more common. They have a mottled brown and grey color, and can become lighter or darker to blend in with their surroundings. Gobies can be identified by their round heads and eyes that bulge out on the top. Their pelvic fins are fused together into one suction-cup-like fin, which they use to cling to rocks in heavy current.
History
Though the precise origin of round gobies in the Great Lakes is not known, the most likely scenario involves gobies hitching a ride in contaminated ballast water aboard vessels entering the lakes from overseas. Gobies are native to the Black Sea and other areas of Eurasia, where natural predators keep their population in check. But gobies have spread rapidly since being released into the Great Lakes. By 2004 they had spread from the St. Clair River all the way to the Eastern Basin of Lake Ontario and the St. Lawrence River.
As of 2011 they are found throughout the Great Lakes system in stunning numbers: as many as 10 billion in western Lake Erie alone, according to scientists from the Ontario Ministry of Natural Resources and the University of Windsor. They have also found their way into many tributaries, and threaten to make their way into inland lakes.
Impact
The full extent of gobies’ impact is not yet known, but in many areas they have decimated native aquatic insect and invertebrate populations. They are prolific spawners, and have invaded the spawning habitat of other fish, which may cause declining numbers of native species. They may be especially harmful to yellow perch, with whom they now directly compete both for food and for spawning habitat.
Gobies also have become a significant part of the diet of many game fish, particularly smallmouth bass and walleye. Gobies are most common in the rocky areas that bass and walleye use as hunting ground, and in many areas gobies are so common that their population is not lessened even by heavy predation. The abundance of gobies has actually led to an increase in game fish size and abundance in parts of the Great Lakes, but they have also caused changes in predatory fish behavior which continually stymie anglers. The diets of smallmouth bass in lakes Erie and Ontario often consist entirely of gobies, and bass can be so well fed that they refuse to strike traditionally effective lures.
Scientists with New York’s Department of Environmental Conservation are also investigating declines in smallmouth bass fishing in Lake Ontario’s Eastern Basin since 2004 – roughly the same time that gobies arrived in the area in significant numbers. At the time of this writing, no methods have been determined to remove gobies from the Great Lakes.