Do low rates of oiled carcass recovery in beached bird surveys indicate low rates of ship-source oil spills?

摘要

Oil pollution is a serious threat to marine ecosystems. Beached bird surveys, which are networks of volunteers who survey beaches for seabird carcasses, are conducted worldwide. Data from these surveys have played a major role in determining that chronically occurring small-scale oil pollution can have cumulative ecosystem-level impacts. Within Canada, Newfoundland and Labrador has reported high rates of oiled carcasses in beached bird surveys (62%), whereas oiled carcass densities in British Columbia are low (12%) compared with Newfoundland and Labrador and other parts of the world. Here, we present a "risk model" as an approach to interpreting beached bird survey data. The model incorporates spatiotemporal distributions of seabirds that are considered vulnerable to oil pollution, shipping densities as a proxy for risk of oil spills, and the proximity of both to areas where beached bird surveys are conducted. Using the model, we identify BC surveys along the west coast of Vancouver Island as most similar to surveys conducted in Newfoundland and Labrador, and we note that 56% of carcasses reported in the BC surveys were oiled, a rate that is similar to rates found in the Newfoundland and Labrador surveys. Finally, we emphasize that wind (speed, direction and persistence) and the location of beach surveys (relative to seabird distributions and high-traffic shipping lanes) must be considered when interpreting beached bird survey results. Because wind data are archived and publicly available, they can be used in reanalyzing older beached bird data from British Columbia. Wind data would also be useful for coordinating future survey efforts, leading to better documentation of the oiling rates of birds off the coast of British Columbia. Finally, our model provides a framework for estimating the risk to seabirds of oiling at sea and for identifying information gaps.