Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water (2011) / Chapter Skim
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to undertake a study to provide technical advice to help inform the derivation of numeric limits for living organisms in ballast water for their regulatory programs. INTRODUCTION Each year there are more than 90,000 visits, on average, of commercial ships greater than 300 metric tons to U.S.
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A final consideration is that much ballast water in the future will be treated to a level beyond what can be accomplished by ballast water exchange, and it is this water that will be the primary target of ballast discharge standards. Studies on the invasion history of North American waters have involved mining occurrence records from the literature and diverse research programs, rather than an organized field-based monitoring program designed explicitly to detect invasions.
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To address Tasks 1 and 2, this report outlines a process of model development and data collection critical to informing future numeric ballast water discharge standards.
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The Convention identifies two key standards; D-1 is a ballast water exchange standard, and the D-2 performance standard sets maximum permissible limits on live organisms in ballast effluent based on the size or taxonomic category of organisms. The statutes that guide the EPA and USCG regulatory programs appear to provide the essential considerations and scope to successfully implement scientifically based numeric standards, given sources of variation (described in Chapter 3)
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Three of the methods discussed are the reaction-diffusion approach, the population viability analysis, and the per capita invasion probability approach -- previously reviewed by EPA for their prospects in helping to set a numeric ballast discharge standard. In principle, a well-supported model of the relationship between invasion risk and organism release could be used to inform a ballast water discharge standard.
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are substantially mismatched in time, and patchy in time, space, and taxonomy; current statistical relationships with these or proxy variables are of dubious value. OTHER APPROACHES TO SETTING A BALLAST WATER DISCHARGE STANDARD In the absence of data and models necessary to support a science-based quantitative approach to setting ballast water discharge standards, expert opinion has been a common alternative.
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Several actions are needed to advance a robust understanding of the risk– release relationship in order to inform future decisions about ballast water discharge standards. As a logical first step, a benchmark discharge standard should be established that clearly reduces concentrations of coastal organisms below current levels resulting from ballast water exchange (such as the IMO D-2 standard)
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Using multiple models with the same data could be valuable to test for concordance. This would also allow one to assess the range of outcomes that would result from proposed ballast water discharge standards.
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Experiments could potentially identify a solid interim basis for discharge standards, noting the inherent challenges in working with a limited number of species and the assumptions that these would be representative of a broad array of potential invasions. Importantly, these data may also have direct application to other vectors, in addition to ballast water, as they test basic questions about establishment that are relevant to propagule pressure arising from all vectors.
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* To date, there has been no concerted effort to collect and integrate the data necessary to provide a robust analysis of the risk–release relationship needed to evaluate invasion probability associated with particular ballast water discharge standards.
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