Great Lakes Article:

A tiny, unwanted alien has invaded a lake in Greater Toronto and wildlife biologists are warning there may be more lurking in the weeds.

At least one rudd, an invasive baitfish originally from Europe, has found its way — likely via the U.S. — into Lake Wilcox in Richmond Hill.

Ministry of Natural Resources biologists say it is the first time rudd, discovered in the Great Lakes in the early '90s, has been found in an Ontario inland lake. This black-sheep member of the minnow family competes with native fish for food and destroys the spawning and nursery habitats of fish like the northern pike, muskellunge and yellow perch.

Although only a single rudd was captured alive in Lake Wilcox in late October, wildlife biologists say there could be more and they will resume monitoring the lake in the spring.

Lake Wilcox is the headwaters for the Humber River, which flows into Lake Ontario through Toronto. This means if there is more than one rudd in Lake Wilcox, it could easily migrate through the Humber to Toronto's shoreline.

It is suspected the fish was carelessly dumped out of a bait bucket into Wilcox. Illegal in Canada as a baitfish, rudd have been used for that purpose in the U.S., where they were introduced in the 1920s.

"When these kinds of things happen, they threaten our natural biodiversity," said Mark Heaton, a fish and wildlife biologist with Ontario's Ministry of Natural Resources.

Rudd, which can grow to 38 centimetres and weigh up to 1.8 kilograms, inhabit warm, shallow, shoreline areas with lots of vegetation. Rudd eat mainly aquatic vegetation and insects.

They can also crossbreed with the native golden shiner, which could effectively wipe out that fish as a separate species if rudd were to spread to other lakes.

Rudd isn't the first non-indigenous species to invade Ontario lakes.

The sea lamprey, which travelled on its own from the Atlantic Ocean, wreaked havoc in Lake Erie in the early 1940s. Most recently, zebra mussels spread like wildfire through the Great Lakes region when ships dumped their ballast. More than 160 non-native species live in the Great Lakes basin.

Heaton says Lake Wilcox is already in bad shape through phosphorus overloads caused by leaking septic systems. This has depleted the oxygen levels in deep waters, leading to massive winter fish kills.

Large mouth bass, shiners, white suckers, carp and as many as 200 northern pike are in Lake Wilcox. The northern pike are especially vulnerable because they live and spawn in the weeds, on which the rudd feed.

David Donnelly, a lawyer with Environmental Defence, calls the growth in invasive species "one of the greatest threats to biodiversity in Ontario waters."

Donnelly said the invaders tend to crowd out indigenous species, leading to fluctuations in numbers.

This, in turn, causes what Donnelly calls a "species wobble," with population decreases following on the heels of explosions. "And the whole natural balance gets out of whack," Donnelly adds.

Beth Brownson, senior invasive species biologist with the ministry, said getting rid of an invasive species can be difficult if not impossible once they take root in another environment.

"The public needs to be really vigilant," she added.

Ministry officials are considering erecting signs on Lake Wilcox asking residents and anglers to be on the lookout for rudd and to call a hotline number if any are spotted.

The signs will also warn anglers that rudd are an illegal baitfish in Ontario and to refrain from dumping them in area lakes and streams.

Meanwhile, the Lake Wilcox rudd now resides, preserved, in a specimen jar at the Royal Ontario Museum. Heaton says it will take further study to determine its sex.

The rudd was first discovered in the St. Lawrence River in 1990.

Since then, it has also been found in western Lake Ontario and eastern Lake Erie.