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New Zealand Whale and Dolphin Trust
Our Research/Fishing Impacts last updated 08 June 2005
New Zealand whale and dolphin trust impacts of fishing
hectors dolphin caught in gill net
 

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 in gillnets 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 where bycatch is unsustainable. The most urgent issue at the moment is the critically endangered Hector's dolphin population off the west coast of the North Island.

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

  • 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. (2002) [ISBN 0-12-551340-2].
  • Fletcher, D., Dawson, S. and Slooten, E. Designing a mark-recapture study to allow for local emigration. Journal of Agricultural, Biological and Environmental Statistics (In press).
  • Pichler, F.B. Slooten, E. & Dawson, S.M. 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 (In press).
  • Slooten, E., Dawson, S. and Rayment, W. Quantifying abundance of Hector’s dolphins between Farewell Spit and Milford Sound. Published client report on contract 3076, funded by Conservation Services Levy. Department of Conservation, Wellington http://csl.doc.govt.nz/ dsis35.pdf (2002).
  • Clement, D., Slooten, E., Dawson, S. and DuFresne, S. Line-transect survey of Hector’s dolphin abundance between Farewell Spit and Motunau. Published client report on contract 3075, funded by Conservation Services Levy. Department of Conservation, Wellington, http://csl.doc.govt.nz/CSL3075.pdf (2001).
  • Dawson, S., Pichler, F., Slooten, E., Russell, K. and Baker, C.S. The North Island Hector’s dolphin is vulnerable to extinction. Marine Mammal Science 17 (2): 366-371 (2001).
  • 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.
  • DuFresne, S., Dawson, S.M. and Slooten, E. Line-transect survey of Hector’s dolphin abundance between Timaru and Long Point, and effect of attraction to survey vessel. Published client report on contract 3074, funded by Conservation Services Levy. Department of Conservation, Wellington, http://csl.doc.govt.nz/CSL3074.pdf (2001).
  • Dawson, S., DuFresne, S., Slooten, E. and Wade, P. Line-transect survey of Hector’s Dolphin abundance between Motunau and Timaru. Published client report on contract 3072, funded by Conservation Services Levy. Department of Conservation, Wellington, http://csl.doc.govt.nz/CSL3072.pdf (2000).
  • Slooten, E., Fletcher, D. and Taylor, B.L. Accounting for uncertainty in risk assessment: Case study of Hector's dolphin mortality due to gillnet entanglement. Conservation Biology 14: 1264-1270 (2000).
  • Cameron, C., Barker, R., Fletcher, D., Slooten, E. and Dawson, S. Modelling survival of Hector’s dolphins around Banks Peninsula, New Zealand. Journal of Agricultural, Biological and Environmental Statistics 4(2): 126-135 (1999).
  • Martien, K.K., Taylor, B.L., Slooten, E. and Dawson, S. A sensitivity analysis to guide research and management for Hector’s dolphin. Biological Conservation 90: 183-191 (1999).
  • Dawson, S.M., Read, A. and Slooten, E. Pingers, porpoises and power: Uncertainties with using pingers to reduce bycatch of small cetaceans. Biological Conservation 84(2): 141-146 (1998).
  • Pichler, F., Baker, CS, Dawson, S.M. And Slooten, E. Geographic isolation of Hector’s dolphin populations described by mitochondrial DNA sequences. Conservation Biology 12(3): 676-682 (1998).
  • Slooten, E. and Dawson, S.M. Conservation of marine mammals in New Zealand. Pacific Conservation Biology 2: 64-76 (1995).
  • Dawson, S.M. 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. 1994.
  • Dawson, S.M. And Slooten, E. 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 (1993).
  • Slooten, E., Dawson, S.M. And Lad, F. Survival rates of photographically identified Hector's dolphins from 1984 to 1988. Marine Mammal Science 8(4): 327-343 (1992).
  • Dawson, S.M. 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. 1991.
  • Dawson, S.M. Modifying gillnets to reduce entanglement of cetaceans. Marine Mammal Science 7(3): 274-282. 1991.
  • Slooten, E. and Lad, F. Population biology and conservation of Hector's dolphin. Canadian Journal of Zoology 69: 1701-1707 (1991).
  • Thorpe, C.W., Bates, R.H.T. And Dawson, S.M. Intrinsic echolocation capability of Hector's dolphin Cephalorhynchus hectori. Journal of the Acoustical Society of America 90(6): 2931-2934. 1991.
  • Dawson, S.M. And Thorpe, C.W. A quantitative analysis of the acoustic repertoire of Hector's dolphin. Ethology 86: 131-145. 1990.
  • Dawson, S.M. The high-frequency sounds of free-ranging Hector's dolphins Cephalorhynchus hectori. Reports of the International Whaling Commission Special issue 9: 339-344. 1988.
  • Dawson, S.M. And Slooten, E. Hector's Dolphin Cephalorhynchus hectori : Distribution and abundance. Reports of the International Whaling Commission, Special Issue 9: 315-324 (1988).

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.

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