Estimation and impacts of seabird mortality from chronic marine oil pollution off the coast of Newfoundland

The Grand Banks south off Newfoundland provide year-round feeding habitat for tens of millions of seabirds of numerous species, an abundance and diversity unparalleled in the North Atlantic. Dense ship traffic routes traverse this productive environment as vessels travel the Great Circle Route between Europe and North America. Oiled seabirds have washed up on beaches in Newfoundland for many decades. Most oil on their feathers has been identified as heavy fuel oil mixed with lubricants, the mixture found in the bilges of large vessels. Beached bird surveys conducted between 1984-1999 indicate that the incidence of chronic oil pollution along the southeast coast of Newfoundland is among the highest in world. More than 60% of all dead birds found over the 16-year period had oil on their feathers; 74% during the last five years. Auks, especially Thick-billed Murres (Uria lomvia), are the most affected. -- In an effort to estimate overall mortality of seabirds in winter due to chronic oil pollution in Atlantic Canada, I performed a series of experiments to determine the fate of oiled and unoiled birds at sea and on beaches. First, I determined that carcasses persisted on average for only 3.3 ± 0.1 days on beaches in southeastern Newfoundland, after which they were no longer detectable due to scavenging or burial in the beach substrate. In addition, no differences were found in persistence rates between oiled and unoiled birds. I also determined deposition rates and detection probabilities of bird carcasses on beaches, and developed a model to estimate the number of birds arriving on a beach between periodic surveys. This model only performs well if survey intervals are less than 10 days. Second, I designed a drift block that accurately mimics the movements of a seabird carcass drifting at sea. As drift blocks used in past studies showed little resemblance to actual carcass drift because they were overly influenced by wind, a more realistic drift block was needed to accurately interpret the number of birds that are found dead on beaches. Third, I measured murre carcass sinking rates and found that birds only float 8.2 ± 5.2 days before sinking, but that scavenging is important. Fourth, I carried out extensive drift block experiments using the new block design to determine the proportion of birds that die at sea and reach the shore, taking into account sinking rates of floating carcasses at sea. Recovery rates of blocks dropped at different locations varied, and the best predictor for the proportion of blocks lost at sea was the distance from shore where they were dropped, combined with the cumulative wind direction vector during the first three days following drift block drops. Based on wind patterns observed during the experiment, I was able to estimate wind specific recovery rates and catchment areas for birds that die at sea. Fifth, I constructed a general mathematical Oiled Seabird Mortality Model to assess seabird mortality due to chronic oil pollution along a given coastline. -- I applied the Oiled Seabird Mortality Model to southeastern Newfoundland, based on periodic beached bird surveys conducted during the winters 1998/1999 through 2000/2001 and the parameters I determined earlier. Several assumptions were made to extrapolate seabird mortality due to oil to a large area at sea, and my most robust estimate is that on average, 315,000 ± 65,000 seabirds were killed annually in southeastern Newfoundland due to illegal discharges of oil from ships. Thick-billed Murres that over- winter on the Grand Banks made up 67 % of this kill. I examined the effects of this anthropogenic mortality, in combination with the estimated number of murres killed during the traditional murre hunt in Newfoundland, on Thick-billed Murre populations that breed in the eastern Canadian Arctic, by building a stochastic (demographic and environmental), age-structured, density independent, pre-breeding, Lefkovitch population projection matrix. The model suggested that chronic oil pollution has reduced potential annual population growth by 2.5 %. In combination with a further 2 % reduction in annual growth caused by hunting, these sustained anthropogenic causes of mortality have made Thick-billed Murre populations particularly vulnerable to environmental changes (e.g. global warming, ocean regime shifts). A series of actions are outlined to help reduce chronic oil pollution in Atlantic Canada, including increased year-round enforcement, imposition of minimum fines and higher imposed fines, the establishment of convenient oil disposal facilities on land, and increased education and awareness programs.

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