ASSESSING SEABIRD MORTALITY FROM CHRONIC OIL DISCHARGES AT SEA

Abstract

Chronic marine oil pollution is an ongoing global problem, yet no model currently exists to assess seabird mortality from continuous low-level inputs of oil. Taking into account persistence and detection rates of birds on beaches, and the wind-dependent proportion of birds lost at sea, we present a general mathematical Oiled Seabird Mortality Model (OSMM) to assess seabird mortality due to chronic oil pollution along a given coastline, using birds counted during systematic beached-bird surveys. We applied our OSMM to Newfoundland, Canada, where the incidence of chronic oil pollution is among the highest in world. We estimated that between 1998 and 2000, an average of 315,000 ± 65,000 murres (common [Uria aalge] and thick-billed [U. lomvia]) and dovekies (Alle alle) were killed annually in southeastern Newfoundland due to illegal discharges of oil from ships. Thick-billed murres that overwinter on the Grand Banks made up 67% of this kill. This species already is subject to extensive summer and winter hunting in Greenland, as well as winter hunting in Newfoundland, which harvests an additional 250,000–300,000 birds/year. Although populations remain stable, these levels of sustained mortality make thick-billed murre populations vulnerable to pulse perturbations and ocean regime shifts and hamper our ability to set harvest at sustainable levels.