[1] Natl Oceanog Ctr, Southampton SO14 3ZH, Hants, England
[2] Univ St Andrews, Sea Mammal Res Unit, St Andrews KY16 8LB, Fife, Scotland
[3] British Antarctic Survey, Cambridge CB3 0ET, England
[4] Fisheries & Oceans Canada, St John, NF A1C 5X1, Canada
[5] Fisheries & Oceans Canada, Maurice Lamontagne Inst, Mont Joli, PQ G5H 3Z4, Canada