Post-mortem examination of Great Northern Divers Gavia immer killed in the Prestige oil spill, Galicia, Spain, 2002/03

Abstract

Great Northern Divers Gavia immer collected during the impact assessment of the 2002/03 Prestige oil spill were studied and compared with similar casualties collected during three other major oil spills. It was concluded that adults tend to winter further to the north in Western Europe than juveniles, and that the sexes were evenly represented in all spills. Wing and bill lengths of adults were also compared with those of museum specimens collected during the breeding season in Canada, Greenland and Iceland in an attempt to determine the possible breeding origin of birds wintering in northwest Spain. Wing lengths suggested that Iceland and Greenland were possible breeding grounds, while the incidence of embedded gunshot (18% of adults) further suggested that at least some birds originated from Greenland, where hunting is still legal. However, biometrics and gunshot incidence alone were inconclusive in determining a possible breeding origin. DNA analyses are being considered, including comparisons with gene sequences for this species already available in the GenBank. Mortality during the Prestige oil spill may have affected 18–22% of the total wintering population in Spain. Besides oil-induced mortality, drowning in fishing gear is identified as a real threat in Galicia. A systematic beached bird survey in the region would help determine the relative importance of different causes of mortality in this species.