Mortality in gillnets (and to a lesser extent trawling) is a serious problem for whale and dolphin populations in many parts of the world. In New Zealand, bycatch in gillnets is threatening several Hector’s dolphin populations.

Dolphin bycatch is one of the Trust’s main research projects. Our groundbreaking research on the Hector’s dolphin population at Banks Peninsula showed that bycatch in gillnets was unsustainable, and led to the creation of the Banks Peninsula Marine Mammal Sanctuary. Later research has shown that substantial numbers of dolphins are still caught immediately north, south and offshore of the sanctuary. A major focus of our current research, therefore, is on assessing these impacts.

Based on these studies, we actively promote the extension of the boundaries of the Banks Peninsula sanctuary, and the need to create sanctuaries in other areas.

Our research on the effects of bycatch has included population surveys around the South Island and off the North Island west coast, to estimate population size. Without an accurate population estimate it is not possible to assess the risks caused by bycatch. We are also actively involved in research on survival, reproductive rate, movements, habitat requirements and risk analyses to assess the effects of bycatch on Hector’s dolphins around the country.

Publications and reports

• Slooten, E. Conservation Management in the face of uncertainty: Effectiveness of four options for managing Hector’s Dolphin bycatch. Endangered Species Research 3: 169-179 (2007)
• Slooten, E., Rayment, W.J. and Dawson, S.M. Offshore distribution of Hector’s dolphins at Banks Peninsula: Is the Banks Peninsula Marine Mammal Sanctuary large enough? New Zealand Journal of Marine and Freshwater Research 40(2): 333-343 (2006)
• Rayment, W., Dawson, S.M., Slooten, E. and Childerhouse, S.J. Offshore distribution of Hector’s dolphin at Banks Peninsula. Department of Conservation Research and Development Series, 232, 23 p. (2006)
• Slooten, E., Dawson, S.M., Rayment, W.J. and Childerhouse, S.J. A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species? Biological Conservation 128: 576-581 Available online 18 November (2005)
• Dawson, S.M. and Slooten, E. Management of gillnet bycatch of cetaceans in New Zealand.  Journal of Cetacean Research and Management  7: 59-64 (2005)
• Slooten, E., Dawson, S.M., Rayment, W.J. and Childerhouse, S.J. Distribution of  Maui’s dolphin, Cephalorhynchus hectori maui. New Zealand Fisheries Assessment Report 2005/28,  21p. Published by Ministry of Fisheries, Wellington (2005)
• Gormley, A.M., Dawson, S.M., Slooten, E. and Bräger, S. Capture-recapture estimates of Hector’s dolphin abundance at Banks Peninsula, New Zealand. Marine Mammal Science 21: 204-216 (2005)
• Slooten, E., Dawson, S.M. and Rayment, W.J. Aerial surveys for coastal dolphins: Abundance of Hector’s dolphins off the South Island west coast, New Zealand. Marine Mammal Science 20: 117-130 (2004)
• Dawson, S.M., Slooten, E., DuFresne, S., Wade, P. and Clement, D. Small-boat surveys for coastal dolphins: Line-transect surveys for Hector‘s dolphins (Cephalorhynchus hectori). Fishery Bulletin 201: 441-451 (2004)
• Burkhart, S.M. and Slooten, E. Population viability analysis for Hector’s dolphin (Cephalorhynchus hectori): A stochastic population model for local populations. New Zealand Journal of Marine and Freshwater Research 37: 553-566 (2003)
• Dawson, S.M. 2002. Cephalorhynchus dolphins. pp. 200-203 In: “Encyclopedia of Marine Mammals” (Perrin, W.F., Würisg, B. & Thewissen, J.G.M, eds.). Academic Press. San Diego. [ISBN 0-12-551340-2].
• Fletcher, D., Dawson, S. and Slooten, E. 2002. Designing a mark-recapture study to allow for local emigration. Journal of Agricultural, Biological and Environmental Statistics 7: 586-593.
• Pichler, F.B. Slooten, E. & Dawson, S.M. 2003. Hector’s dolphins and fisheries in NZ: a species at risk? Marine mammals and humans: towards a sustainable balance. N. Gales, M. Hindell & R. Kirkwood (eds), Melbourne University Press.
• Dawson, S., Pichler, F., Slooten, E., Russell, K. and Baker, C.S. 2001. The North Island Hector’s dolphin is vulnerable to extinction. Marine Mammal Science 17 (2): 366-371.
• Dawson, S.M. 2001. Fine-scale abundance estimates from the 2000/2001 aerial survey of Hector’s dolphins on the South Island west coast. DOC Science Internal Series 21. 9 pp. Department of Conservation, Wellington.
• Slooten, E., Fletcher, D. and Taylor, B.L. 2000. Accounting for uncertainty in risk assessment: Case study of Hector’s dolphin mortality due to gillnet entanglement. Conservation Biology 14: 1264-1270.
• Cameron, C., Barker, R., Fletcher, D., Slooten, E. and Dawson, S. 1999. Modelling survival of Hector’s dolphins around Banks Peninsula, New Zealand. Journal of Agricultural, Biological and Environmental Statistics 4(2): 126-135.
• Martien, K.K., Taylor, B.L., Slooten, E. and Dawson, S. 1999. A sensitivity analysis to guide research and management for Hector’s dolphin. Biological Conservation 90: 183-191.
• Dawson, S.M., Read, A. and Slooten, E. 1998. Pingers, porpoises and power: Uncertainties with using pingers to reduce bycatch of small cetaceans. Biological Conservation 84(2): 141-146.
• Pichler, F., Baker, CS, Dawson, S.M. And Slooten, E. 1998. Geographic isolation of Hector’s dolphin populations described by mitochondrial DNA sequences. Conservation Biology 12(3): 676-682.
• Slooten, E. and Dawson, S.M. 1995. Conservation of marine mammals in New Zealand. Pacific Conservation Biology 2: 64-76.
• Dawson, S.M. 1994. The potential for reducing entanglement of dolphins and porpoises with acoustic modifications to gillnets. Reports of the International Whaling Commission. Spec. Issue 15: 573-578.
• Dawson, S.M. And Slooten, E. 1993. Conservation of Hector’s dolphins: The case and process which led to establishment of the Banks Peninsula Marine Mammal Sanctuary. Aquatic Conservation: Marine and Freshwater Ecosystems 3: 207-221.
• Slooten, E., Dawson, S.M. And Lad, F. 1992. Survival rates of photographically identified Hector’s dolphins from 1984 to 1988. Marine Mammal Science 8(4): 327-343.
• Dawson, S.M. 1991. Clicks and Communication: The behavioural and social contexts of Hector’s dolphin vocalisations. Ethology 88(4): 265-276 (1991).
• Dawson, S.M. Incidental catch of Hector’s dolphins in inshore gillnets. Marine Mammal Science 7(3): 283-295.
• Dawson, S.M. 1991. Modifying gillnets to reduce entanglement of cetaceans. Marine Mammal Science 7(3): 274-282.
• Slooten, E. and Lad, F. 1991. Population biology and conservation of Hector’s dolphin. Canadian Journal of Zoology 69: 1701-1707.
• Thorpe, C.W., Bates, R.H.T. And Dawson, S.M. 1991. Intrinsic echolocation capability of Hector’s dolphin Cephalorhynchus hectori. Journal of the Acoustical Society of America 90(6): 2931-2934.
• Dawson, S.M. And Thorpe, C.W. 1990. A quantitative analysis of the acoustic repertoire of Hector’s dolphin. Ethology 86: 131-145.
• Dawson, S.M. 1988. The high-frequency sounds of free-ranging Hector’s dolphins Cephalorhynchus hectori. Reports of the International Whaling Commission Special issue 9: 339-344.
• Dawson, S.M. And Slooten, E. 1988. Hector’s Dolphin Cephalorhynchus hectori : Distribution and abundance. Reports of the International Whaling Commission, Special Issue 9: 315-324.

For a list of general Trust associated publications and reports on marine mammals and marine mammal ecology, click here. To find out about some of the people involved in this research, see the University of Otago Marine Mammal Research Group web site.