Research Document - 2013/128
National Risk Assessment for Introduction of Aquatic Nonindigenous Species to Canada by Ballast Water
By O. Casas-Monroy, R.D. Linley, J.K. Adams, F.T. Chan, D.A.R. Drake, and S.A. Bailey
Abstract
Ballast water has been identified as a major vector for introduction of aquatic nonindigenous species (NIS) into and within Canada, although a series of regulatory changes enacted in the past decade may have slowed the rate of ballast-mediated invasions. We conducted a national risk assessment to better understand the relative invasion risk posed by ballast water discharges across Canada by different merchant shipping pathways (e.g., transoceanic, coastal and domestic). We assess current risk (under present ballast water exchange (BWE) requirements) and future risk (under international ballast water discharge standards) at two scales: annual invasion risk and risk per discharge event. The potential for introduction of NIS and the magnitude of consequences of introduction are estimated considering shipping activity (ballast volume discharged), propagule pressure (based on biological sampling surveys), environmental similarity between donor and recipient ports (based on salinity and climate), the number of high impact NIS in donor ecoregions, and effects of mitigation strategies (BWE or discharge standards). The invasion risk currently posed by International Transoceanic vessels in the Great Lakes-St. Lawrence River (GLSLR) region was used as the “lowest risk” benchmark, since BWE is thought particularly effective for this pathway and no ballast-mediated NIS have been reported from the Great Lakes since 2006; however, even lowest risk pathways pose a risk of invasion.
Although few ballast water discharges occur in the Arctic, resulting in a relatively low annual risk, the risk posed by individual discharges of International Transoceanic vessels in the Arctic is comparatively high. Arctic ports are unlikely to serve as a source of NIS for other Canadian waters. Ships operating within the Ballast Water Exemption Zones in the Pacific and Atlantic regions currently pose a relatively high invasion risk. International Exempt vessels are an important pathway for the introduction of zooplankton and phytoplankton NIS into Canadian waters through the transport of un-exchanged ballast water. The risk of domestic vessels is variable across regions, taxa and timescales. Lakers pose a relatively high risk for zooplankton NIS, while Eastern Coastal Domestic vessels pose a relatively high risk for both taxa on an individual discharge basis. The risk posed by domestic ships in the Arctic is relatively low, while Pacific Coastal Domestic vessels were not assessed due to lack of data. While current regulatory requirements for ballast water exchange by transoceanic vessels reduce the risk of invasions to freshwater ecosystems (e.g., Great Lakes), these regulations are less effective in reducing the risk to marine ecosystems. The risk of introducing zooplankton NIS would be reduced for all pathways if managed in accordance with the IMO D-2 standard. However, the risk of introducing phytoplankton would only be reduced for five pathways. We caution that all risk results should be interpreted only as relative among ballast pathways in Canada. The absolute risk posed (i.e., probability of invasions/year due to ballast activities) is currently unknown because of the uncertain nature of the propagule pressure-establishment relationship.
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