Mass mortality of seabirds in the aftermath of thePrestigeoil spill

Ignacio Munilla,Daniel Oro,Alberto Velando,José Manuel Arcos,David Álvarez,Patricia M. Leyenda

doi:10.1890/es11-00020.1

Abstract

In the winter of 2002–03 the Prestige tanker spilled 60,000 tons of oil over the northern half of the Iberian Coastal Large Marine Ecosystem (northern Portugal to France). Most (c. 85%) of the 22,981 oiled seabirds reported were alcids (i.e., auks): Common Murres (Uria aalge), Razorbills (Alca torda) and Atlantic Puffins (Fratercula arctica). Here we estimated the mortality of alcids in Galicia (northwestern Spain), the area that received most of the Prestige oil and where half of the oiled seabirds were collected. We performed three experiments that included: (1) a test of several drift block models in open sea, to select the one that best fitted the drift of alcid carcasses; (2) the release of 450 drift blocks at 9 offshore points to assess the recovery rate of oiled alcids and its spatial variation; (3) the assessment of beach survey effort and the detectability of drift blocks. Mean mortality estimates and their bootstrapped confidence intervals were obtained through an estimation model that established: (1) a temporal limit of 23 days to block drifting; (2) spatial differences in the recovery rates of blocks depending on how far away from the coast they were released; (3) a correction factor accounting for detectability, and (4) the distribution pattern of the three alcid species involved according to three distance classes, based on ship surveys. The Prestige oil spill, in terms of acute seabird mortality, was one of the worst oil spills ever reported worldwide. Compared to other major oil spills the estimated mortality for the Prestige oil spill was higher than expected from the number of carcasses retrieved. We recommend that drift block assessments of seabird mortality should be included in contingency response plans to oil pollution emergencies; therefore, a supply of drift-blocks designed to mimic the drifting behavior of the marine bird species of interests should be at hand.

Highlights

Large oil spills are dramatic examples of largescale perturbation pulses in marine ecosystems as they increase exposure to toxic compounds in marine organisms over a wide area (Salomone MUNILLA ET AL.2002)
We recommend that drift block assessments of seabird mortality should be included in contingency response plans to oil pollution emergencies; a supply of drift-blocks designed to mimic the drifting behavior of the marine bird species of interests should be at hand
Atlantic Puffins tended to aggregate near the shelf edge whereas the majority of Razorbills and Common Murres were observed less than 10 km from the coastline

Summary

Introduction

In common with other pulse perturbations, large oil spills often result in rapid alterations of the density of one or more members of the communities affected (see Bender et al 1984) This appears to be true in the case of seabirds. Of all impacts on wildlife, the oiling of seabirds probably attracts the greatest public and scientific concern (e.g., Dunnet 1982, Wiens et al 1984, Salomone 2002) Due to their high vulnerability and exposure, marine birds are amongst the most conspicuous victims of oil spills at sea and they are considered as suitable bioindicators of marine oil pollution (Furness and Monaghan 1987, Perez et al 2008, Munilla and Velando 2010, Velando et al 2010). The impacts of oil spills commonly extend over wide spatial scales and may combine with environmental factors to cause fluctuations in seabird populations (Votier et al 2005, 2008)

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Discussion

Conclusion