Science Advisory Report 2019/003

Science advice on the effectiveness of ballast water exchange plus treatment as a mechanism to reduce the introduction and establishment of aquatic invasive species in Canadian ports

Summary

• Ballast water is a high-risk vector for the introduction of aquatic invasive species (AIS). AIS cause profound ecological changes, including biodiversity loss, changes in trophic dynamics, loss of fishery productivity, and introduction of disease. As a result of these ecological changes, invasions modify ecosystem services and generate direct and indirect economic damages.
• The following Science Advisory Report (SAR) is based on a model-based analysis of shipping and biological data to understand the implications of different management strategies (no management, ballast water exchange (BWE), ballast water treatment, and exchange plus treatment) across different regions in Canada. 
• Two metrics were developed to assess establishment risk: the per trip probability that at least one species invasion occurs, and the number of species invasions per year. The number of species per year reflects the outcome of the per trip probability of invasion when shipping traffic is considered. To simplify the interpretation of results, these invasion metrics were converted to the number of trips until at least one species invasion occurs and the number of species invasions per decade.
• In general, when all vessels in this study adhere to the D-2 standard, the use of ballast water management systems (BWMS) is expected to provide a substantial reduction in establishment risk compared to BWE, for both assessment metrics.
• For the Great Lakes-St. Lawrence River (GLSLR) region, maintaining exchange in addition to treatment when the ballast source is brackish or fresh water would result in a lower number of harmful phytoplankton invasions than transitioning to a strategy that only uses BWMS.
• Exchange plus treatment would further reduce the risk of establishment compared to treatment alone for the GLSLR region when ballast water is treated using BWMS on all or half of the ship-trips. When all vessels meet the D-2 standard, the expected number of species per decade (SpPD) decreases from 1.61 (BWMS alone) to 1.28 (exchange plus treatment) for zooplankton and 0.61 (BWMS alone) to 0.45 (BWE plus BWMS) for phytoplankton. When BWMS are used on 50% of voyages, SpPD decreases from 5.15 (BWMS alone) to 4.52 (BWE plus BWMS) for zooplankton and 1.41 (BWMS alone) to 1.07 (BWE plus BWMS) for phytoplankton.
• For all other pathways in Canada, exchange plus treatment has variable effects compared to treatment alone. The most consistent risk reduction of adding exchange to treatment was observed for voyages destined to freshwater ports from freshwater or brackish source ports. Exchange plus treatment is less effective than treatment alone for voyages originating from marine ports and terminating in freshwater ports when 100% of transits meet the D-2 standard.
• In the event that only 50% of transits meet the D-2 standard, exchange plus treatment provides an important reduction in establishment risk compared to treatment alone when the ballast source is fresh water.

This Science Advisory Report is from the February 27-28, 2018 Science advice on ballast water exchange plus treatment. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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