Research Document - 2015/037
An ecological and oceanographical assessment of alternate ballast water exchange zones in the Canadian eastern Arctic
By D.B. Stewart, S.H. Nudds, K.L. Howland, C.G. Hannah, and J.W. Higdon
Abstract
Mid-ocean exchange of ballast water is recommended for vessels entering Canadian waters from outside Canadian jurisdiction to minimize the risk of ballast-mediated transfer of nonindigenous species (NIS). When this cannot be accomplished due to inclement weather or other circumstances, designated alternate ballast water exchange zones (ABWEZ) within Canadian waters may be used. Vessels entering Canadian waters to load commodities, such as iron ore in the eastern Canadian Arctic, may increase greatly by 2020. This study evaluates the relative risks from exchange at different locations in the eastern Canadian Arctic, including existing ABWEZs in Lancaster Sound and Hudson Strait, using a coupled-ice-ocean model with meteorological forcing and particle tracking.
In the model, ballast water discharge was simulated as the release of particles along vessel tracks into the surface layer of circulation models for Baffin Bay – Labrador Sea and Lancaster Sound. Particle transport provided metrics for comparing relative likelihood of exposure. The receiving habitats were differentiated and weighted for comparison based on relative likelihood of establishment and relative habitat sensitivity. The final relative risk to receiving habitats from ballast water exchange along each ship track was then calculated from the product of the likelihood of exposure, likelihood of establishment, and habitat sensitivity. Since the relationship between survival of NIS and various environmental parameters has not been empirically demonstrated in this region, different weighting scenarios were used to test the sensitivity of the model to establishment and habitat sensitivity metrics. The model was robust to these different weightings and consistently identified the same regions as having higher relative risk.
The modelling results indicate that existing ABWEZs in and around Lancaster Sound and Hudson Strait are among the areas of highest relative risk for introductions of NIS via ballast water. Lower risk portions of major vessel tracks should be considered as alternatives, including the Labrador Sea portion of all vessel tracks, and the Baffin Bay deep offshore vessel track at depths greater than 1000 m. Foreign coastal biota released along these tracks are least likely to reach shallow coastal habitats that offer favourable conditions for their survival and establishment. To further mitigate risks from organisms in the ballast sediment, it is recommended that vessels entering the Canadian Eastern Arctic from outside Canada’s Exclusive Economic Zone (EEZ) not in ballast flush their residuals from the ballast tanks prior to entering waters under Canadian jurisdiction. Further research is recommended to assess the risk of species introductions associated with ballast water exchange in the Canadian Arctic, the effectiveness of exchange for reducing risk associated with the release of ballast water into the region’s coastal waters, and options for ballast exchange by vessels operating within the EEZ.
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