Background/Question/Methods The Laurentian Great Lakes have been a hotspot of biological invasions by non-indigenous species (NIS), many of which are associated with commercial shipping and the use of ballast water. Consequently, beginning May 1993 all vessels entering the Great Lakes with ballast water from sources outside of Canada and the U.S. Exclusive Economic Zones (EEZ), foreign ballast water, were required to conduct mid-ocean ballast water exchange (BWE) to reduce the propagule pressure by physical removal and osmotic stress. All previous efforts to characterize the ballast water vector in the Great Lakes were based on relatively small sample sizes or used proxies for estimating ballast water flux (e.g. cargo tonnage). We used three years of data from two independent sources, ballast water reports submitted to the U.S. Coast Guard via the National Ballast Information Clearinghouse (NBIC) and vessel movement records from the Canadian Coast Guard Information System on Marine Navigation (INNAV).

Results/Conclusions For vessels that also operated beyond the Great Lakes and St. Lawrence Seaway (the Great Lakes System), we quantified the vessel activity and associated ballast water operations while they operated in the Great Lakes System from 2005-2007. During this three-year period, 417 vessels reported 2256 arrivals to NBIC, with the annual totals ranging between 700-800 arrivals in the Great Lakes System. Most vessels entering the Seaway < 5 times; however, there are a few domestic vessels (i.e. Canadian or U.S. flagged) that report more than 100 arrivals in the Great Lakes System during this period. Vessels that operate beyond the Great Lakes System discharged more than 435,000 MT of foreign ballast water, of which 94% underwent BWE. In addition, these vessels reported discharging more than 600,000 MT of ballast water that was entrained beyond the Great Lakes System but within the Canadian and U.S. EEZs, of which approximately 25% underwent BWE. The largest ballast fluxby these vessels , greater than 7,500,000 MT, was the movement of ballast water between lakes. Over two thirds of the intra-lake flux was from Lake Ontario to Lake Erie. Lake Superior received the greatest volume of foreign ballast water and received ballast water entrained in each of the other lakes. The propagule pressure from foreign sources has been greatly reduced by the use of BWE; however, there remains a large flux of unmanaged domestic ballast water into and within the Great Lakes System.