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UBC Theses and Dissertations

Underwater aliens : quantifying propagule pressure of aquatic invasive species in Canadian shipping ports Lo, Veronica Bethany Pui Gwun


Increased trading worldwide has created introduction pathways for aquatic invasive species (AIS), particularly through shipping activities. In our research, we used ballast discharge data and estimates of the wetted surface area of vessels to provide preliminary estimates of the potential propagule pressure ballast and hull fouling organisms on Canadian shipping ports from the commercial shipping sector. We compared total wetted surface area, vessel arrivals and ballast discharge across shipping ports and vessel categories in the Atlantic, Great Lakes-St. Lawrence and Pacific shipping regions. Using these potential propagule pressure estimates for ballast organisms, we developed a model, building on that of MacIsaac et al.’s (2002), to characterize the effective propagule pressure of aquatic non-native species to Canadian shipping ports. Our model includes the effects of environmental similarity between destination and source on mortality, which can be considerable. We parameterized the model using recent nationally and regionally collected databases on ship voyages, and abundance surveys yielding mortality rates of several zooplankton species. These empirically derived parameters were used in our model to predict abundances of live individuals after ballast is discharged, with estimates of uncertainty and sensitivity to key assumptions. Our results indicate that for our three shipping regions, aggregate wetted surface area, vessel arrivals, and total ballast discharge were significantly correlated across shipping ports (Spearman’s ρ ranged from 0.57 to 0.87, p<0.05). Correlations between these measures of propagule pressure were more variable and of varying levels of significance across vessel categories (Spearman’s ρ ranged from 0.43 to 0.98). Our modeling results demonstrate that variation in mortality rates across tanks and voyages resulted in high variation in total effective propagule pressure. The variation between tanks and voyages has important implications for the use of mid-ocean exchange as a ballast management method for different ports and species. To our knowledge, our characterization of potential and effective propagule pressure from the commercial shipping sector is the first to be conducted on a nation-wide scale. Our propagule pressure estimates will contribute to future efforts to determine the relationship between the establishment of aquatic invasive species and the environmental similarity between source and discharge areas.

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