Invasive Species

"Extinction is forever, so is the introduction of Exotic Species."(Ted Gannon, SOLEC Conference, 2002)

All species are native to some region where they function as part of the ecosystem of that region. However, when species from one region are introduced into a different region, with different ecosystems, they can wreak havoc. Species that are non-native to a particular region are also referred to as invasive species. These species are often invasive because there are no natural predators or limiting conditions, enable the species to flourish. Often this uncontrolled growth can cause other native species to decline.

Several new species have been introduced into Lake Simcoe, with important impacts on the aquatic ecosystem. The earliest species that was introduced was the common carp more than a century ago. Their abundant numbers are thought to have contributed to the destruction of extensive wild rice beds that formerly flourished in the lower Holland River and Cook's Bay. Carp may also have been responsible for the destruction of other fish spawning and nursery habitats.

The Rainbow Smelt are another introduced species and they were first observed in the early 1960's. They were believed to compete with native Lake Whitefish and somewhat responsible for a decline in their populations. However, in recent years the smelt populations themselves have declined probably as a result of Lake Trout, which view the smelt as a food source.

Black crappie, zebra mussels and the spiny water flea are other species that have been recently introduced to the lake. The numbers of all of these species have increased rapidly since their introduction. The effects of these invaders on other aquatic species have not yet been revealed, but significant changes are expected. The effects on water quality, however, are starting to be revealed and the results are not encouraging.

For example, it is believed that zebra mussels have had a major effect on Lake Simcoe water quality by dramatically improving water clarity. Zebra mussels are small fresh water mollusks native to the Black and Caspian seas. They were transported to the Great Lakes in the ballast tanks of ships and first appeared in Lake Simcoe in 1994. Zebra mussels are filter feeders, screening and removing biota and particles floating in the water. This filtering activity is responsible for the improvement in water clarity and possibly a slight reduction in phosphorus concentrations within the water.

The improvement in water clarity resulting from the zebra mussels has substantially increased the area where the sunlight can penetrate onto the lake bottom (Euphotic zone). This increase in has promoted the widespread growth of bottom rooted aquatic plants especially near the shoreline. The problem has become so severe in many areas that landowners continuously have to remove truckloads of dead aquatic vegetation that is washing up along their shorelines. This has had a disastrous impact on recreational opportunities and even negatively influenced property values.