1. a WWF Responsible Fisheries Programme, WWF South Africa , PO Box 50035, Waterfront , 8001 , South Africa
2. b DST/NRF Centre of Excellence at the Percy FitzPatrick Institute of African Ornithology , University of Cape Town , Rondebosch , 7701 , South Africa
3. c Animal Demography Unit, Department of Zoology , University of Cape Town , Rondebosch , 7701 , South Africa