1. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Science Center, Marine Mammal and Turtle Division, 8901 La Jolla Shores Drive, La Jolla, California 92037, USA
2. Cooperative Institute for Marine Resources Studies, Oregon State University and National Ocean and Atmospheric Administration Pacific Marine Environmental Laboratory, 2030 Marine Science Drive, Newport, Oregon 97365, USA
3. Centre for Research into Ecological and Environmental Modelling, University of St Andrews, St Andrews, Fife, KY16 9LZ, United Kingdom
4. Ocean Associates, Incorporated, 4007 North Abingdon Street, Arlington, Virginia 22207, USA