INVASION MADE SMALLMOUTH FISHING A WHOLE NEW BALLGAME

The Round Goby is a bottom-dwelling fish native to central Eurasia, including the Black Sea and the Caspian Sea. Round gobies have established large non-native populations in the North American Great Lakes and tributary waters. They are a small, soft-bodied fish with a distinctive black spot on the first dorsal fin. The eyes are large and protrude slightly from the top of the head and the pelvic fins are fused to form a single disc shaped like a suction cup on the belly. Gobies range in length from 4 to 10 inches and weigh just a couple ounces. Males are larger than females. Juveniles are grey, and adults become mottled with grey, black, brown, and olive green markings. Adult males turn inky black during the spawning season and develop swollen cheeks.

Since 1990, the round goby has been registered as being “introduced” into the North American Great Lakes as an invasive species. They are also rapidly expanding into tributaries of the Great Lakes such as the Erie Canal, Lake Oneida, and the Finger Lakes of New York such as Cayuga Lake. They are commonly found on flats and shelves with sandy and rocky bottoms with low silting. Their primary diet includes mollusks (think zebra mussels), crustaceans, worms, fish eggs, small fish, insect larvae, and other small invertebrates living on the bottom.

Female gobies reach sexual maturity in one to two years while males do so in three to four years. In the Great Lakes it has been observed that they mature up to one year earlier than in their native European habitat. Females can spawn up to six times during the spawning season, which spans April to September. Males will migrate from deeper water into shallower breeding grounds during the beginning of the mating season. They then release a pheromone that attracts females to their territory. Males also use visual displays such as posturing and changing color during mating season, and can produce sounds during courtship. The females deposit their eggs in male-guarded crevices between rocks, and their egg clutches can contain up to five thousand eggs. Males are territorial and will defend eggs from predators as well as continuously fan the developing embryos, a behavior which helps result in hatch rates up to 95%.

The story goes that gobies were accidentally introduced into North America by way of ballast

water from cargo ships. They were first discovered in North America in the St. Clair River in 1990, and from the beginning there were concerns of significant ecological and economic impact from competition with native species. The goby is an aggressive fish that can outcompete native sculpins and log perch for snails and mussels, shelter, and nesting sites. Round gobies are also predators of eggs of native fish. They are robust, and can survive in degraded environmental conditions.

The good news has been that many native predatory fish such as smallmouth, largemouth, walleye, salmon, and trout prey heavily on gobies. Another beneficial factor is that they have helped control the population of zebra mussels, preventing the type of large-scale spread of zebra mussels, also an invasive species, than was originally feared. It is clear from the increased size of smallmouth catches in Lake St Clair, Lake Erie, Lake Ontario and the St. Lawrence River, that the goby has had a positive impact on recreational fishing. Many bait manufactures specialize in producing goby imitators that have become very popular baits.