Round gobies are a bottom-dwelling fish that can reach 10 inches in length. They have been known to steal bait from fishing lines and are unintentionally caught by anglers.
Round gobies were first discovered in the St. Clair River in 1990 and have spread rapidly in the Great Lakes and some inland lakes.
Once established, gobies can displace native fish, eat their eggs and young, take over optimal habitat, spawn multiple times per season and survive in poor quality water.
The round goby is native to the Black and Caspian Sea regions and was introduced to the Great Lakes through ballast water. Although adult gobies spend their lives near the bottom; however, larval gobies swim to the surface at night and are easily sucked into ballast tanks. This contributed to the rapid spread of gobies to ports around the Great Lakes after their initial discovery in the St. Clair River in 1990. The non-native round goby is considered an invasive species because of the negative impact they have had on the Great Lakes ecosystem.
Competition with Native Fish
The mottled sculpin, a native species, and the round goby look and act similarly. Yet, the goby is much more aggressive than the mottled sculpin, and as a consequence, the sculpin has been virtually eliminated in some areas where the goby has invaded. Other small, bottom-dwelling fish — including johnny darter and logperch — have also suffered.
Although competition for food is often assumed to be the primary negative impact of non-native species, this does not appear to be the case with sculpin and goby. Instead, gobies chase male sculpin from the nests they guard and seize the sites for themselves, putting more pressure on sculpin and reproductive survival.
Round goby colonized shallow nearshore habitats of the Great Lakes first, and their effects on nearshore fish have been the subject of much research. Gobies are now moving into deeper habitat (extending more than 360 feet deep!) and far upstream into trout streams and warm-water rivers. One research project suggests that goby may be less problematic in Wisconsin streams, but more study is needed as they continue to spread to and multiply in new habitats.
Ability to Feed on Other Invasives
Zebra mussels — from the same area gobies originate from — arrived shortly before the round goby in many Great Lakes habitats. Researchers found that goby prey heavily on zebra mussels, which leads to a variety of changes in everything from mussels to algae. Gobies will not completely eliminate zebra mussels because they generally avoid the largest mussel shells and cannot effectively feed on mussels that grow between rocks. However, they can reduce mussel numbers to some extent, particularly where mussel numbers are high.
Gobies also reduce numbers of several other invertebrates, either through predation or through removal of mussels that provide hiding spots. They even affect the amount of algae that grows on rocks. In the short term, they appear to increase algae through indirect effects, but they have the potential to decrease filamentous algae (single algae cells that form long visible chains or threads that intertwine, forming a mat that resembles wet wool) through reduction of zebra mussels over the long term. In Green Bay, habitats with mussels but without gobies had 12 times more algae than habitats that had been colonized by both mussels and gobies for at least one year.
Most studies have concentrated on goby effects in shallow Great Lakes habitats; however, the rapid expansion of both round goby and quagga mussel into deep waters of Lake Michigan raises new questions. The Green Bay study found that gobies did reduce quagga numbers, and quaggas may be more vulnerable than zebras because they do not require attachment to rocks that can also provide refuge from gobies. In Lake Ontario, another study found that gobies caught in 180 to 310 feet of water fed heavily on mussels, but goby diet shifted to the native opossum shrimp — a primary food source for several native species — in deeper water.
New Food Source for Gamefish
Tournament bass anglers have long known that gobies are a favorite food of smallmouth bass in Great Lakes bays and connecting waters. Other nearshore species like walleye, yellow perch and brown trout also prey heavily on gobies at times. Now that the goby has spread to deeper, colder habitats, lake trout are feeding on them, too. In Lake Huron, gobies were very abundant when alewife numbers crashed in 2004. Chinook salmon, which focus on eating open-water preyfish, did not learn to switch their diet to bottom-dwelling gobies.
Role in Botulism Outbreaks
Gamefish aren’t alone in taking advantage of the round goby as a new food source. Water snakes, cormorants, loons and even the threatened lake sturgeon have developed an appetite for them. The downside of this is that gobies are implicated in outbreaks of Type E botulism that resulted in the death of 7,500 birds in Lake Michigan during 2007.
However, factors behind recent botulism outbreaks are not fully understood and they do not occur every year. It appears that mussels accumulate the botulism toxin, which is produced by a bacterium that grows in areas where oxygen is depleted by rotting algae. Gobies eat the mussels and pass the toxin along to whatever eats them.
Gobies develop ‘hyperpigmentation’ when exposed to the botulism toxin. This begins as splotches of black coloration, and can result in the entire fish turning black before dying. Heat destroys the toxin, so anglers are not at risk of contracting botulism if fish are cooked before eating. Pet owners should be aware that cats or dogs that eat dead fish or birds along the shore of Lake Michigan could be at risk.
Potential for Control
Once an invasive species becomes as widespread and abundant as the round goby has become in the Great Lakes, no possibility of complete eradication exists. The goby has become a permanent fixture in the Great Lakes food web, but researchers have taken some preliminary steps toward control measures appropriate for localized populations.
Bottom-release formulations of fish poisons have potential for small-scale selective control of round gobies and a pheromone found in the urine of reproductive male gobies may eventually be developed as a control tool. Seismic guns — equipment that uses sound frequencies and water jets to blast away invaders — have also been used in attempts to drive gobies off of spawning reefs where they prey on native fish eggs, but to date these experimental techniques have not been successful enough to form the basis of ongoing control programs.
At this time, efforts to limit the spread of goby focus primarily on educating anglers and others who might spread gobies, and other invasives, to new areas. Precautions like draining the livewell and bilge after leaving a body of water, disposing of unused bait in the trash or compost pile, and not transferring live fish from one body of water to another are important in preventing the spread of exotics.
If you catch a round goby in an inland lake or stream you can check the GLANSIS website to see if goby have been found in that location before. If not, please report it using the GLANSIS form.