Ontario's waterways under attack

Ontario's waterways under attack

Many inland waters, no less than the oceans, have suffered from environmental threats, often from invading species released by seagoing freighters in their ballast water.

In the Great Lakes alone, some 180 invasive species have established themselves. Here are a few of the invaders that have found haven in Ontario's waterways and what methods of control, if any, have been found.

Zebra mussels, native to the Black and Caspian Sea regions of Asia, are now widespread throughout the Great Lakes and in many smaller lakes of North America. They arrived in the mid 1980s, presumably in ballast water.

With few natural predators and a high reproductive rate, zebra mussels have clogged water intake pipes along lake shorelines, often cutting off factories, lakeshore homes and even boats from their water sources.

By filtering out phytoplankton, they have made lakes inhospitable for certain tiny species, especially Diporeia, a shrimp-like organism that is an important food source for whitefish, smelt, sculpin and young lake trout from various Great Lakes. As these fish have declined, so have the numbers of sport fish that prey on them, including salmon, trout and walleye.

Zebra mussels have squeezed out many native clam colonies. In their vast accumulation, they have also damaged navigational markers, fishing buoys, fishing nets, and boat hulls.

The zebra mussel does millions of dollars' worth of damage every year. Scientists have not had much luck eradicating them. The best recourse is to prevent their spread from one body of water to another.

The round goby is the most common invasive species in the Great Lakes, and is now spreading to other lakes, including, just recently, Lake Simcoe. It also was carried to the Great Lakes in ballast water from the Caspian region. Since they feast on zebra mussels, their initial growth in numbers was explosive. They frequently feed on the eggs of other fish such as smallmouth bass and wild perch, and those sports fish have declined significantly in number. The round goby are easily caught and, because of their small size, fishermen often take them for bait for use in other lakes, which contributes to their spread throughout the smaller lakes. Scientists have not found an effective control method.

Lamprey eels were introduced into the Great Lakes in the early 20th century through shipping canals. Lakes Michigan and Huron are the most badly effected. Sea lamprey fasten onto large fish with a sucking disk and feed on their bodily fluids. All fish species are attacked, including lake trout, salmon, rainbow trout, whitefish, walleye and sturgeon. The lake trout fishery in Lakes Huron and Superior used to yield seven million kilograms annually, but by the 1960s, that figure had fallen by 98 per cent, largely due to the sea lamprey.

Remediation in this case has been huge effective, with certain chemicals proving effective as lampricides. Sea lamprey numbers have been reduced by 90 per cent and some fisheries have rebounded nicely.

The European frog-bit, a plant that resembles a water lily, is found throughout Eastern Ontario wetlands and is spreading west.