Research Document - 2012/116
Relative Risk Assessment for ship-mediated introductions of aquatic nonindigenous species to the Atlantic Region of Canada
By J.K. Adams, S.M. Ellis, F.T. Chan, J.E. Bronnenhuber, A.G. Doolittle, N. Simard, C.H. McKenzie, J.L Martin, S.A. Bailey
Abstract
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. A number of high impact NIS have established in the Atlantic region of Canada during the past two decades, with the coastal waters around Prince Edward Island now being one of the most heavily invaded marine ecosystems in Canada. A series of regulatory changes enacted by Canada in the past decade may have slowed the rate of ship-mediated invasions 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 commercial ports in Atlantic Canada and the Gulf/Estuary of St. Lawrence; a subsequent national risk assessment will utilize data from the regional risk assessments to examine risk from a ‘pathway’ perspective. The risk posed by a NIS is the product of the probability of introduction and the consequences of introduction. 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 Atlantic ports 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 Atlantic ports through shipping activities. The probability of introduction and potential magnitude of consequences were then combined for a final invasion risk rating. Finally, we identify priorities and make recommendations for future management needs.
A transit analysis shows that Atlantic ports are connected with international and domestic ports, resulting in potential for species transfers via hull fouling and ballast water discharge from foreign ports as well as through secondary spread. The final relative invasion risk for nonindigenous species via hull fouling was higher for Dartmouth-Halifax (Nova Scotia), intermediate for Canso-Mulgrave – Point Tupper (Nova Scotia), Saint John (New Brunswick), Blacks Harbour (New Brunswick), North Head (New Brunswick), Saint-Siméon (Québec), Rivière-du-Loup (Québec), Isle-aux-Grues (Québec), and Matane (Québec), and lower for all remaining top Atlantic ports. The final relative invasion risk for nonindigenous species via ballast water was higher for Sept-Îles (Québec), intermediate for Come By Chance-Whiffen Head (Newfoundland), Port-Cartier (Québec), Saint John (New Brunswick), and lower for all remaining top Atlantic ports. It is important to note that estimated invasion probabilities and risk ratings presented in this document are relative, and that rankings of “lower” or “lowest” do not indicate zero risk.
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