Gobies on the Move

Round gobies, invasive fish that have spread quickly throughout Lakes St. Clair, Huron, Ontario, and Erie and slowly through Lake Simcoe and the Kawarthas are now making their way into Great Lake's tributaries, threatening their aquatic ecosystems and species that are rare or at risk.

"They're starting to move into river systems, which is odd, since they're not really a riverine fish," said University of Toronto Researcher Mark Poos, whose work was part of a 5-year study on gobies that drew from research conducted by the MNR, the Department of Fisheries and Oceans, and the Ontario Federation of Anglers and Hunters (OFAH).

Poos says 17 of 19 species of bottomdwelling fish and 6 of 36 species of mussels in those waters are known or suspected of being affected by the goby invasions. "They out-compete and predate on the young of other fish and impact mussel reproduction by affecting host fish species."

Included are the eastern sand darter, which is threatened, and six endangered mussels. Moreover, gobies have been found in the Thames and Sydenham Rivers, which contain the largest diversity of species at risk in Canada.

Two theories on their range expansion are being considered, says Poos. "One is that there are two different genetic strains of round gobies, with one being more adventurous and adaptable. The other suggests they're simply overcrowded in the waters they're in."

Anglers shouldn't release caught gobies or transfer bait into different waters. "Once they're in inland rivers, they can become a threat to inland lakes, too, he said."