They're small, they're slippery and they don't belong here. And a team of McMaster University researchers is analyzing how the round goby is causing a problem.

McMaster's Aquatic Behavioural Ecology Lab is doing its annual summer monitoring of round goby populations in Hamilton Harbour. Next year, the lab will release an updated report on the local prevalence of the fish — namely regarding its apparently stabilizing population.

“It does seem that there is a plateau in (the population), but we've only looked at a period of eight years,” said Sigal Balshine, professor in the department of psychology, neuroscience and behaviour. “But we'll know the answer to that shortly.”

The round goby is native to Eurasia, particularly the Black Sea and Caspian Sea. It was introduced to the Great Lakes through the ballast water of ships. The first confirmed sighting in Lake Ontario was in 1998.

The goby has been destructive because of it is more aggressive than native fish and competes for the same food source. It also spawns more often than fish local to the Great Lakes.

When it was introduced, it had no natural predators. But that appears to be changing, Balshine said.

Her team's initial report about four years ago analyzed the population from 2000 to 2008, which followed a boom and apparent plateau of the round goby population.

Right now, Balshine's team of students and volunteers collects samples from the harbour and around Cootes Paradise every two weeks. From May until October, the team looks at six sampling sites to examine the goby's abundance, fitness and sex ratio.

The population could be stabilizing because more predators have discovered and are eating the goby, said Erin McCallum, a graduate student on the team.

“Other fish may be eating gobies now, as well as predatory birds like cormorants and water gulls,” she said.

“Realistically, I don't think you'll ever get rid of gobies. They're well established throughout the Great Lakes and they continue to invade the streams and tributaries surrounding them. But we can keep track of what's going on.”