1. Department of Biology; Dalhousie University; Halifax NS B3H 4JI Canada
2. Population Ecology Division; Department of Fisheries and Oceans; Bedford Institute of Oceanography; Dartmouth NS B2Y 4A2 Canada
3. Department of Biological Sciences; Macquarie University; Sydney NSW 2109 Australia
4. Sea Mammal Research Unit; Scottish Oceans Institute; University of St. Andrews; St. Andrews KY16 8LB Scotland
5. Vemco; 20 Angus Morton Drive Bedford NS B4B 0L9 Canada