Quantification of Risks of Alien Species Introductions Associated with Ballast Water Discharge in the Gulf of St. Lawrence

Canada has one of the longest navigable coastlines in the world, bordering the Atlantic, Arctic and Pacific Oceans, as well as the Great Lakes. Shipping is important to the Canadian national and international trade. Our coastal waters receive yearly over 52 million tonnes of ballast water from foreign ports around the world [Gauthier and Steel (1966) Canadian Manuscript Report of Fisheries and Aquatic Sciences 2380: 1-57]. Millions of tonnes of ballast water are discharged into the estuary of the St. LawrencesRiver and into the Gulf of St. Lawrence each year [Bourgeois et al. (2001) Rapp. Tech. Can. Sci. Halient Aquat. 2338; viii +34p]. Ballast water has been identified as one of the pathways by which alien aquatic species are introduced outside of their normal range. Under the current Canadian voluntary guidelines, all ships entering Canadian waters are expected to exchange ballast water outside of the Exclusive Economic Zone (EEZ). The 2001 Transport Canada survey showed that 77% of all ships entering the Gulf of St. Lawrence have exchanged ballast water in mid-ocean. Of the remainder, 8.5%were ships that traveled up the North American coastline and declared themselves exempt from the need to exchange. An additional 13% did not have a clear reason for not exchanging and may in fact also be part of the coastal trade. Less then 1% of all ships surveyed declared safety as a reason for not doing the exchange. The current guidelines make provisions for ballast water exchange in 'back-up areas' if, for safety reasons, exchange is not feasible offshore. Incoming foreign ships may exchange their ballast water within the Gulf of St. Lawrence and in the Laurentian Channel southeast of Anticosti Island,where the depth exceeds 300 m. The magnitude of the risk such ballast water exchanges pose, compared to risk from ballast water discharge in other areas of the Gulf of St. Lawrence, was evaluated using a probabilistic risk assessment (PRA) model. The risk was measured in terms of quantity of alien species introduced into various parts of the Gulf, including the Laurentian Channel, given current shipping patternsand practices. The relative risk to the Laurentian Channel is 0.5% of the quantity of alien species introduced in the Gulf and Estuary as a whole (including the Laurentian Channel). As the model also calculates the quantity of alien species introduced into other discreet areas of the Gulf of St. Lawrence and the freshwater estuary, it shows that under current