MEPS 318:271-276 (2006)  -  doi:10.3354/meps318271

Sex-specific mortality of European shags after the Prestige oil spill: demographic implications for the recovery of colonies

Alejandro Martínez-Abraín1,*, Alberto Velando2, Daniel Oro1, Meritxell Genovart1,4, Cati Gerique3, Miguel Angel Bartolomé3, Elena Villuendas3, Blanca Sarzo3

1IMEDEA (CSIC-UIB), C/Miquel Marqués 21, 07190 Esporles, Majorca, Spain
2Departamento de Ecoloxía e Bioloxía Animal, Facultade de Ciencias, Campus Lagoas-Marconsende, Universidade de Vigo, 36310 Vigo, Spain
3Centro de recuperación de fauna Granja de El Saler, Conselleria de Territorio y Vivienda, Avda. de los Pinares 106, El Saler, 46012 Valencia, Spain
4Sezione di Biologia Evolutiva, Dipartimento di Biología, Universita’ di Ferrara, Via Borsari 46, 44100 Ferrara, Italy

ABSTRACT: Oil spills are extreme environmental perturbations (i.e. ecological catastrophes) affecting marine food webs and especially top predators, in which effects are likely amplified. As such, seabirds suffer from direct mortality and food depletion, with potentially important consequences for the population growth rate and probability of extinction. However, little is known about the effects of sex-skewed mortality (due to sex spatio-temporal differences in at-sea distribution) in seabird population dynamics. We analyzed the mortality of European shags Phalacrocorax aristotelis after the Prestige oil spill and its effects on breeding colonies in Galicia (southwest North Atlantic). Most adults found dead were females (85%). The year after the spill, Monte Carlo simulations of population trajectories predicted a reduction of 11% in the number of breeding pairs when skewed mortality was considered, and a lower rate (8%) when assuming random sex distribution of adult mortality. The further reduction predicted with the sex-biased mortality was probably the result of unmated adults unable to reproduce. This difference, although slight, is a concern for conservation owing that the colonies studied were already showing a 5% annual decline due to other factors also related to human activities.

KEY WORDS: Skewed mortality · Sex · Oil spills · Demographic consequences · Prestige · Shags

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