Abstract

species fe a tu re Ontario, covering an area of 2.8 million km2 (1.1 million miles2), is one of the largest jurisdictions in North America (Figure 1). There are in excess of 250,000 inland lakes, thousands of kilometres of streams and rivers, and waters of 4 of the Laurentian Great Lakes within the province of Ontario. It has been estimated that Ontario accounts for approxi-mately 15 % of the world’s freshwater. Ontario waters are known to support 165 species of fish, 128 of which are native species (Mandrak and Crossman 1992). One of the most pressing ecological issues today involves the transfer and spread of non-indigenous species. Non-indigenous species may be defined as plants or animals which are transferred to areas out-side of their historic or natural geographic range (Fuller et al. 1999). Invasive aquatic species can have profound eco-nomic and ecological impacts. An estimated $500 million is spent annually by Canada on efforts to con-trol invasive aquatic species in the Great Lakes (Commissioner of the Environment and Sustainable Development 2001). MacIsaac (2003) estimated costs of up to $750 million annually for damage to aquatic ecosystems in Canada. Worldwide, the impact of invasive aquatic organisms is estimated to cost more than $314 billion per year in damage and control costs (Pimentel 2002). From an ecological perspective, invasive species can often cause major disruptions to native fauna. Native species may be reduced in numbers, driven to extinction directly by competition and predation, or be genetically altered by hybridization with non-indigenous species. Invasive aquatic species are considered to be one of the major threats to fish species at risk in the Great Lakes area (A. Dextrase,