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Research Document - 2011/104

Risk Assessment for ship-mediated introductions of aquatic nonindigenous species to the Great Lakes and freshwater St. Lawrence River

By S.A. Bailey, F. Chan, S.M. Ellis, J.E. Bronnenhuber, J.N. Bradie, and N. Simard


Ballast water has historically been the predominant ship-mediated vector for aquatic nonindigenous species (NIS) introductions to Canada, while hull fouling is recognized as a leading sub-vector for the introduction of marine aquatic NIS worldwide. At least 182 aquatic NIS have established in the Great Lakes, making this one of the most highly invaded ecosystems globally. A series of regulatory changes enacted by Canada and the United States have slowed the rate of invasion and facilitated changes in invader characteristics. The objective of this report was to conduct a relative risk assessment of shipping vectors (hull fouling and ballast water) to the freshwater ports in the Great Lakes and the St. Lawrence River (GLSLR). First, the probability of introduction was estimated by combining the individual probabilities of successful transition through each stage of the invasion process (i.e., arrival, survival and establishment) based on ship arrival/ballast water discharge data and environmental conditions at GLSLR and potential source ports. Second, the potential magnitude of consequences of introduction was estimated based on the number of high impact ship-mediated NIS recorded for eco-regions of ports directly connected to GLSLR ports through shipping activities. The probability of introduction and potential magnitude of consequences were then combined for a final relative invasion risk rating. Finally, we identify priorities and make recommendations for future management needs.

A transit analysis shows that GLSLR ports are connected with international and coastal domestic ports, resulting in potential for species transfers via hull fouling and ballast water discharge. Laker vessels (those that operate exclusively in the GLSLR) appear to be the most important transport pathway of fouling and ballast-mediated NIS in the region. The final relative invasion risk for fouling NIS is intermediate for Montréal (Québec), Québec City (Québec) and Duluth-Superior (Minnesota-Wisconsin), and lower for the remaining top ports, with moderate uncertainty. The final invasion risk for ballast-mediated NIS is higher for Duluth-Superior, intermediate for Québec City and Montréal, and lower for the remaining top ports, with moderate uncertainty. It is important to note that results presented in this document are based on relative rankings among GLSLR top ports. Ports identified as higher risk in this study may not be high risk in a national scale considering the relatively low international shipping traffic in the region; these ratings will be recalibrated to differentiate risk among top ports from all Canadian regions in a subsequent national risk assessment.

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