and the introduction of nonnative species of animals and plants. Billions of dollars and uncounted hours have been spent in addressing these and other stresses and their impacts on the Great Lakes ecosystem.

Given that the Great Lakes form a single system of interconnected lakes and rivers, it is widely acknowledged that many of the stresses imposed on the system by human activity can only be addressed effectively on a systemwide basis (see, for example, U.S. Environmental Protection Agency and Government of Canada 1995). The Great Lakes system of governance, however, is fragmented among the agencies, offices, and organizations of two federal governments; eight states; two provinces; and myriad municipalities, local governments, and aboriginal peoples. As a result, it has been suggested that the institutional capacity to halt either new or reemerging stresses is lacking (International Joint Commission 2003).

This report focuses on one of the many stresses imposed on the Great Lakes by human activity: the introduction of aquatic invasive species (AIS) through maritime trade. Also referred to as introduced, alien, exotic, nonnative, or nonindigenous, an invasive species, which may be aquatic or terrestrial, is defined as one transported by human activity into a region where it did not occur in historical time and where it is now established in the wild. Not all introduced species are invasive, in the sense of being harmful, very abundant, or spreading rapidly. However, the term “AIS” has been widely adopted by the press, politicians, and the public, and for that reason it is used throughout this report, except in quoting sources that use alternative terminology.

Recent reports estimate the number of AIS in the Great Lakes at more than 180, including algae, fish, invertebrates, and plants (Ricciardi 2006). There are many agents, or vectors, by which such species enter the Great Lakes, including commercial shipping, recreational boating, angling or bait fishing, aquaculture, commercial and home aquaria, water gardens, canals, and rivers. The focus of this report is commercial shipping, and in particular vessels transiting the St. Lawrence Seaway.

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