Research Document - 2013/043
Relative Risk Assessment for ship-mediated introductions of aquatic nonindigenous species to the Pacific Region of Canada
By R.D. Linley, A.G. Doolittle, F.T. Chan, J. O'Neill, T. Sutherland and 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. Ninety-four aquatic NIS have established in the marine waters of Canada’s Pacific coast, 78 of which were recorded near the port of Vancouver in the Georgia Strait. A series of regulatory changes enacted by Transport Canada in the past decade may have slowed the rate of ship-mediated invasions and favoured changes in invader characteristics. The objective of this report is to conduct a relative risk assessment of shipping vectors (ballast water and hull fouling) to ports in the Canadian Pacific region; 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 Pacific 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 Pacific 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 Canadian Pacific ports are connected with international ports, resulting in potential for species transfers via hull fouling and ballast water discharge. The final relative invasion risk for hull fouling-mediated NIS is higher for Vancouver and lower for all remaining top ports, with high uncertainty. The final relative invasion risk for ballast-mediated NIS is higher for Vancouver and lower for all remaining top ports, with moderate uncertainty. 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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