1. Environmental Research Division/Southwest Fisheries Science Center/National Marine Fisheries Service/National Oceanic and Atmospheric Administration, Monterey, CA 93940, USA.
2. Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 94923, USA.
3. Marine Mammal Institute, Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA.
4. Southall Environmental Associates, Aptos, CA 95003, USA.
5. Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA.