Effects of the Iron Baron oil spill on little penguins (Eudyptula minor). I. Estimates of mortality

Abstract

The bulk ore carrier Iron Baron ran aground on Hebe Reef at the mouth of the Tamar River in northern Tasmania, Australia, on 10 July 1995. It released an estimated 325 tonnes of bunker fuel oil. Of the wildlife species affected, the most readily detected was the little penguin (Eudyptula minor); 1894 were collected and treated for oiling. This study estimates the impact of the oil spill on populations of little penguins. At Ninth Island (approximately 40 km from Hebe Reef), one of the most affected little penguin colonies, pre-oil-spill population estimates were available. Extensive regular trapping and mark–recapture of birds at this site during the course of the oil spill provided longitudinal data on oiling rates from a known population size. Using these data, we estimate that 19.6% of birds from Ninth Island were oiled and survived to come ashore. This represents about 526 (1932–3108, 95% CL) adult birds, or up to 5566 (4197–6917) birds in total (adults and juveniles). For estimates of the impact on little penguin populations in the region, we provide three scenarios of the possible numbers of penguins oiled. After considering the biases of each risk assessment, we believe that between 10 000 and 20 000 penguins were killed as a result of the oil spill. The study indicates that, despite the relatively small amount of oil spilt by the Iron Baron, the impact on penguin populations was extensive. This study also highlights the difficulties and requirements in assessing the impact of oil spills on wildlife populations.