1. National Center for Ecological Analysis and Synthesis, University of California, 735 State Street, Suite 300, Santa Barbara, CA 93101-3351, USA
2. Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia
3. School of Biological Science, University of Sydney, Sydney, New South Wales 2006, Australia
4. Sea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife KY16 8LB, UK
5. Marine Biology and Ecology Research Centre, School of Marine Science and Engineering, Plymouth University, Plymouth PL4 8 AA, UK
6. IMARES, PO Box 167, 1790 AD Den Burg-Texel, The Netherlands