New Zealand fur seals and fisheries
Marine mammals, especially seals and sea lions are seen by commercial fishers as competitors for fish. In New Zealand concern about the number of fur seals, and their impact on fishing has led to periodic calls for the population to be culled. At present this species is protected in New Zealand waters, except for bycatch in fishing. New Zealand fur seal numbers appear to be increasing, and they have been found to be re-colonising part of their earlier habitat.
As a result, the Department of Conservation contracted us to carry out research into NZ fur seal diet to investigate whether the species is having an impact on target fishing species. Data for this study were derived from seal scats and vomits collected from colonies in the Foveaux Straight area, the Snares Islands, and in northern Fiordland. The data gathered from this work are more complete as they were collected over several seasons.
Seals eat a commercially fished species of arrow-squid, however they target a much smaller size than is gathered by the fishing industry, and their other prey species are of little or no interest to commercial and recreational fishers. The conclusions of this study were made available to conservation managers, and for public education.
Bycatch of marine mammals in fishing operations has become an issue of great international concern. The last twenty years have seen a spectacular increase in middle depth and deepwater trawl fisheries in New Zealand, with a corresponding increase in the bycatch of marine mammals. Substantial numbers of New Zealand fur seals and New Zealand sea lions are killed in these fisheries each year. Data on the population biology of both species are limited and because of this the impact of the bycatch cannot be estimated reliably. Key parameters which are currently unknown for both species include age at sexual maturity, birth rate, maximum age, and annual survival rate. Current population size of fur seals is also unknown.
Key researcher: James Holborow
Bejder, L. and Dawson, S.M. Abundance, residency and habitat utilisation of Hector's dolphins in Porpoise Bay, New Zealand. New Zealand Journal of Marine and Freshwater Research 35: 277-287. 2001.
Bräger, S., Dawson, S.M., Slooten, E., Smith, S., Stone, G.S. and Yoshinaga, A. Site fidelity and along-shore range in Hector’s dolphin, an endangered marine dolphin from New Zealand. Biological Conservation 108: 281-287 (2002)
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)
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)
Darby, J.T. and Dawson, S.M. Incidental bycatch of yellow-eyed penguins (Megadyptes antipodes) in gillnets in New Zealand waters 1979-1997. Biological Conservation 93(3): 327-332. 2000
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. 2002. Cephalorhynchus dolphins. pp. 200-203 in: “Encyclopedia of Marine Mammals” (Perrin, W.F., Würsig, B. & Thewissen, J.G.M, eds.). Academic Press. San Diego. 2002 [ISBN 0-12-551340-2]
Dawson, S.M. and Lusseau, D. Pseudoreplication problems in studies of dolphin and porpoise reactions to pingers. Marine Mammal Science 21(1). 175-176. 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)
Dawson, S.M. Dolphins and whales. Pp.336-338 in The Natural History of Southland (Darby, J.T, Fordyce, R.E, Mark, A., Probert, K., and Townsend, C.R. eds), Otago University Press. Dunedin. 2003. [ISBN 877133-51-5]
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)
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)
Dickie, G.S, and Dawson, S.M. Age, growth and reproduction in New Zealand fur seals. Marine Mammal Science 19(1): 173-185. 2003.
Fletcher, D., Dawson, S. and Slooten, E. Designing a mark-recapture study to allow for local emigration. Journal of Agricultural, Biological and Environmental Statistics 7(4): 1-8 (2002)
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)
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)
McConkey, S.D., Lalas, C., and Dawson, S.M. Moult and changes in body shape and pelage in known-age male New Zealand sea lions. New Zealand Journal of Zoology 29:53-61. 2002.
Pichler, F., Baker, C.S., 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)
Pichler, F.B., Slooten, E. and Dawson, S.M. Hector’s dolphins and fisheries in NZ: a species at risk? Pages 153-173 In: Marine mammals and humans: towards a sustainable balance. N.J. Gales, M.A. Hindell & R. Kirkwood (eds), Collingwood, Victoria, CSIRO (2003)
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. Conservation management in the face of uncertainty: Effectiveness of four options for managing Hector's dolphin bycatch. Endangered Species Research 3: 169-179 (2007) www.int-res.com/journals /esr/esr-home/
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)
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)
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)
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)
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)