1. John H. Prescott Marine Laboratory, New England Aquarium, Central Wharf, Boston, MA 02110, USA
2. Biology Department, Boston University, Boston, MA, USA
3. Sea Mammal Research Unit, University of St Andrews, St Andrews, UK
4. Department of Environmental Conservation, University of Massachusetts, Amherst, MA, USA
5. Office of International Affairs, NOAA Fisheries, Silver Spring, MD, USA