Research Document 2020/003
Effectiveness of Ballast Water Exchange plus Treatment as a Mechanism to Reduce the Introduction and Establishment of Aquatic Invasive Species in Canadian Ports
By Drake, D.A.R., Bradie, J.N., Ogilvie, D., Casas-Monroy, O., and Bailey, S.A.
Abstract
The movement of ballast water is a prominent pathway for the dispersal of harmful aquatic species. As a continuous effort to better prevent invasions via this high-risk pathway, the current management strategy of ballast water exchange (BWE) will be gradually replaced by the International Maritime Organization's D-2 ballast water performance standard with the use of onboard ballast water management systems (BWMS). The Canadian Government proposed using BWE in concert with BWMS as this strategy may provide additional protection to certain ecosystems. Research on the performance of this strategy is required nationally and across different habitat types, so that informed decisions may be made on its implementation in Canada.
This study conducted a model-based analysis to estimate the invasion rate of non-indigenous zooplankton and harmful phytoplankton species via ballast water discharge in Canada under various ballast management strategies, with the objective to assess the relative performance of exchange plus treatment against exchange or treatment alone. Four management strategies were modelled: no management, BWE, ballast water treatment, and exchange plus treatment. Treatment was modelled by applying the D-2 standard on either all or half of the voyages to evaluate its effectiveness under different ballast water discharge compliance rates. These management scenarios were applied to five shipping pathways in Canada (i.e., Pacific International, Atlantic International, Great Lakes-St. Lawrence River (GLSLR) International, Arctic International, and Arctic Domestic). The management scenarios were also assessed on a port salinity basis, as environmental conditions such as salinity are known to influence the effectiveness of BWE.
The effectiveness of exchange plus treatment compared to treatment alone varied among shipping pathways and habitat types. With all vessels adhering to the D-2 standard, exchange plus treatment was the most effective management strategy at mitigating non-indigenous zooplankton establishments in GLSLR International and Arctic International, while exchange plus treatment did not provide additional invasion risk reduction for either taxonomic group over treatment alone for the other shipping pathways. For the source and recipient port salinity combinations, exchange plus treatment provided the greatest reduction in species establishment risk when the ballast source was either fresh or brackish water and the destination port was fresh water, while the efficacy of exchange plus treatment and treatment alone were similar for all other source and recipient port salinity combinations. When the D-2 standard was applied to only 50% of voyages, exchange plus treatment substantially decreased establishment risk when the ballast source was fresh water, regardless of the salinity of the recipient environment.
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