1. Sea Mammal Research Unit, University of St Andrews, St Andrews, Fife KY16 8LB, UK
2. Centre d'Etudes Biologiques de Chizé, CNRS, 79360 Villiers en Bois, France
3. Wildlife Conservation Society, Argentina and Marine Programs, Amenábar 1595, 1426 Buenos Aires, Argentina
4. Centro para el Estudio de Sistemas Marinos, CONICET, Boulevard Brown 2915, 9120 Puerto Madryn, Chubut, Argentina
5. Department of Biology, Aarhus University, 8000 Aarhus, Denmark