[1] Univ Calif Santa Cruz, Long Marine Lab, Santa Cruz, CA 95060 USA
[2] Sonoma State Univ, Dept Biol, Rohnert Pk, CA 94928 USA
[3] NOAA NMFS, Antarctic Marine Living Resources Program, Southwest Fisheries Sci Ctr, La Jolla, CA 92037 USA
[4] Univ St Andrews, Sea Mammal Res Unit, St Andrews KY16 8LB, Fife, Scotland