Population trends and reproductive success of the European shag Phalacrocorax aristotelis on the Iberian Peninsula following the Prestige oil spill

In 2003, immediately following the Prestige oil spill in Galicia, Spain, we studied the population trends and reproductive performance of European shags (Phalacrocorax aristotelis) at oiled and unoiled colonies. This bird is an important member of the nearshore marine community, breeding in the area affected by the Prestige oil spill. The European shag feeds around the breeding colonies throughout the year, making it a useful indicator of environmental change. Before the oil spill, population trends were similar between oiled and unoiled colonies. Nevertheless, colonies located within the path of the oil suffered greater declines (ca. 10%) compared with pre-spill trends and with population trends at unoiled colonies. In 2003, the breeding success was 50% lower in oiled colonies compared with unoiled colonies. The data available from pre-spill years suggest that the annual reproductive success did not differ among colonies before the impact. European shags breeding at colonies affected by oil showed a negative initial impact from the Prestige oil spill. The reduction in reproductive success at oiled colonies may be due to sub-lethal effects of oil exposure or low food availability after the oil spill.