ON Nature, Winter 2009/2010
by Sharon Oosthoek
Round gobies were first discovered in the St. Clair River in 1990, likely arriving through ballast water from ocean-going ships.
Fisheries biologists have unexpectedly discovered round gobies in the Thames, Sydenham, Ausable and Grand rivers and are now sounding the alarm over how this invasive fish may affect endangered species.
The Great Lakes tributaries were long thought to be immune to such an invasion thanks to their status as Canada’s most diverse aquatic ecosystem. It was thought that since each ecological niche was taken up, invaders could not gain a foothold.
But a team of scientists from the universities of Toronto and Guelph, and the Ontario Ministry of Natural Resources, stumbled across the round gobies starting in 2006 while checking on the health of various tributaries in southwestern Ontario.
“We didn’t anticipate finding round gobies. That wasn’t the goal of the work,” said Mark Poos, a PhD student in biology at the University of Toronto.
Poos is lead author of a recent study showing that gobies can potentially harm up to 89 per cent of fish species and 17 per cent of mussel species in the tributaries.
Round gobies push other fish, such as the threatened eastern sand darter, out of their spawning beds and will in some cases eat their eggs, thereby reducing their populations.
Gobies threaten mussels more indirectly, by decreasing the number of fish on which they rely when they’re young.
Young mussels, such as the endangered snuffbox mussel, attach themselves to the gills of at-risk fish. Without the help of their hosts, they couldn’t move from one river system to another, their geographical ranges would shrink, and a single catastrophe could wipe out an entire species of mussel.
Round gobies were first discovered in the St. Clair River in 1990, likely arriving through ballast water from ocean-going ships. But until recently, they hadn’t found their way into the Great Lake’s tributaries.
“It truly is a new invasion,” said Poos. “The question is why. That’s the one thing I don’t think we have a handle on.”
There are some educated guesses, however.
Perhaps the goby population has now grown large enough to push its way into the tributaries. Or maybe there are two genetic types of gobies – one of which is more invasive than the other – and it’s the hyper-invasive type that has now made its way into the Great Lakes system.
Whatever the cause, scientists such as Poos hope to influence those who fish in the Great Lakes’ tributaries not to transfer bait – which could include gobies – caught in one area to another.
“We’re not entirely sure what’s going to happen,” says Poos. “These fish and mussel species are already getting hit by other things – habitat alteration and turbidity. So when a new species comes in that can compete with them, I think it poses a serious problem.”