Seminar Title: Thirty-five years of progress on the Great Lakes: from no policy to global ballast water standards

Abstract: Expert opinion has placed invasive species as a top stressor of the Great Lakes.  Up until the late 1980s, ballast water - the principal pathway (65% of invasions) for species introduction to the system – was unregulated. Invasions by zebra mussels and Eurasian ruffe focused attention of researchers and policy makers on the ballast water threat, resulting in a 1993 USCG policy mandating ballast water exchange (BWE) for vessels entering the system with filled ballast tanks. A retrospective analysis of reported invasions 13 years before and after implementation of the policy shows that new ballast-mediated invasions was virtually unchanged (16 vs 15 species, respectively). Further policy change in 2006 (Canada) and USA (2008) required even vessels with residual ballast water to ‘flush’ open-ocean water through tanks before entry, and coincided with a dramatic decline in new invasions (2 species) over the following 13-year period. This decline is best explained by policy change and not by alternative explanations (shipping volume, source pool depletion, search effort). The International Maritime Organization is presently implementing a new global policy (IMO D-2) based on abundance-based performance standards for different size classes of introduced organisms. The theory behind this policy is based on the well-established principle of ‘propagule pressure’, which defines risk based on the concentration of viable organisms discharged of a single species.  However, IMO D-2 is based on ‘community propagule pressure’, a nebulous and unstudied concept, and it ignores the conflating influence of colonization pressure (ie. the number of species introduced).  Here I will show that at the concentration of organisms relevant to IMO D-2, colonization pressure has a much greater influence on probability of invasion than ‘community propagule pressure’. I will also examine compliance with the new IMO D-2 standard for  zooplankton, and suggest safeguards for the Great Lakes to ensure that vessels do not exceed permissible abundance discharge limits.