Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, Washington, USA;3. National Institute of Water and Atmospheric Research Ltd., Christchurch, New Zealand;4. Department of Fisheries and Wildlife, Marine Mammal Institute, Oregon State University, Newport, Oregon, USA;5. Farallon Institute, Petaluma, California, USA;6. Commonwealth of the Northern Mariana Islands Department of Lands and Natural Resources, Saipan, Northern Mariana Islands, USA;7. Department of Fisheries and Wildlife, Hatfield Marine Science Center, Oregon State University, Newport, Oregon, USA;8. Health and Biosecurity, Commonwealth Scientific and Industrial Research Organisation, Townsville, Queensland, Australia;9. British Antarctic Survey, Natural Environment Research Council, High Cross, Cambridge, UK