Vessel biofouling as a vector for nonindigenous species introductions in Canada

Biofouling is the accumulation of organisms (such as algae, mussels, barnacles, and other taxa) on underwater surfaces. Biofouling on vessels is seen as undesirable, as it reduces vessel fuel efficiency through increased drag, and has potential to transfer organisms over long distances to locations outside their natural biogeographic region. Compared to other vectors that transfer aquatic organisms, such as ballast water, biofouling is relatively understudied despite being a major contributing vector of aquatic nonindigenous species (NIS) to coastal ecosystems globally. As a result, Transport Canada requested science advice from Fisheries and Oceans Canada, seeking an updated national assessment of the probability of NIS introduction and establishment via biofouling on vessels, to inform the development of biofouling management policies. This study used a multistage mechanistic model (a multiple-step model describing the parts or stages of the invasion process) to assess the probability of introduction and establishment of NIS into Canada based on one year of data on first arrivals of foreign-flagged commercial vessels. The stages in the model included arrival, survival, and establishment of NIS, but throughout this document the term ‘establishment’ denotes the cumulative success through all three stages to result in a self-sustaining population in Canadian waters. Separate assessments were conducted for vessels’ main hull surfaces and combined niche areas (such as the sea chest, propeller, and thruster tunnels, where biofouling may be more concentrated). Results were summarized for the four coastal regions of Canada based on the destination/arrival port of the vessels: Atlantic, Pacific, Great Lakes-St. Lawrence River, and Arctic regions. The model parameters were based on empirical vessel biofouling and environmental data, as well as estimates of biological processes with variability introduced. Estimates of mean NIS primary establishments per year via vessel hulls ranged from <1 (Arctic region) to 2.2 (Pacific region). Similarly, the mean number of trips until at least one NIS establishment is successful via the hull ranged from 94 (Pacific region) to 174 (Great Lakes-St. Lawrence River region). Primary NIS establishments via vessel niche areas were generally higher than those associated with the hull, with the highest species establishments per year being 8.4, with 23 trips until establishment occurs (Pacific region). While there is uncertainty associated with these estimates, these results indicate a meaningful probability of NIS establishments by vessel biofouling in all regions of Canada. The Atlantic and Pacific coasts are expected to receive the greatest numbers of NIS establishments, driven by the higher number of vessel arrivals to these regions. NIS establishment rates via the main hull areas of vessels were lower compared to niche areas, with the niche areas (all combined) having higher abundance of biofouling but smaller wetted surface area. Vessel biofouling should be considered as a dominant, active vector for introduction of NIS to Canada.

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