The Great Lakes of the United States have been subjected to adverse ecological and economic impacts from nonindigenous species (NIS). Ballast water from commercial shipping is the major means by which NIS have entered the Great Lakes. To help resource managers assess the future arrival and spread of invasive species, 58 species were initially identified as having a moderate or high potential to spread and cause ecological impacts to the Great Lakes. Using a species distribution model (the Genetic Algorithm for Rule-Set Production or GARP), areas within the Great Lakes where 14 of these 58 potential invasive species could find suitable habitat, were identified. Based on the model and species depth tolerances, all of Lake Erie and the shallow water areas of the other four Great Lakes are most vulnerable to invasion by the 14 modeled species. Analysis of ballast water discharge data of vessels entering the Great Lakes via the St. Lawrence Seaway revealed that the original source of most ballast water discharges came from Canada and Western Europe. The Great Lakes ports at greatest risk for invasion by the 14 modeled species from ballast water discharges are Toledo, Ashtabula and Sandusky, OH; Gary, IN; Duluth, MN; Milwaukee and Superior, WI; and Chicago, IL. Since early detection is critical in managing for NIS, these results should help focus monitoring activities on particular species at the most vulnerable Great Lakes ports. This assessment demonstrates that successful invasions are best predicted by knowing the propagule pressure (i.e., the number of larvae/individuals entering a new area) and habitat matching (i.e., how similar is the invaded area to the native range of the species).

"EPA/600/R-08/066F." "November 2008." Includes bibliographical references.