1. Sea Mammal Research Unit; University of St Andrews; East sands St Andrews KY16 9LB Scotland
2. Department of Animal Biology; La Laguna University; Astrofísico Francisco Sánchez La Laguna 38206 Tenerife Spain
3. Centre for Research into Environmental and Ecological Modeling; University of St Andrews; The Observatory Buchanan Gardens; St Andrews KY16 9LZ Scotland
4. Pelagic Ecology Research Group; Scottish Oceans Institute; University of St Andrews; East sands St Andrews KY16 9LB Scotland