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Abundance estimation of
inshore dolphins and whales
A nationwide population survey for Hector's
dolphins was carried out between 1998 and 2004. We used a 15m catamaran (see Dawson
et al.,
2004) and a high-wing plane (Slooten et al. 2004) to carry out
line-transect surveys. Helicopters were used to
estimate the proportion of dolphins
counted (e.g. by recording the amount of time dolphins spend at the water surface).
As a result, we now have
an up-to-date and robust estimate of
Hector's dolphin abundance around the
South Island of 7,270 (CV 16.2%). There are an estimated 111 (CV 44%) North Island Hector's dolphins, also known as Maui's dolphins. For more detailed information, see the references listed below. Information about abundance and distribution of the dolphins is vital for the management of
this endangered species.
Data from these surveys
have also been used to provide advice on survey design. Line transect methods
are used successfully on many shipboard
marine mammal abundance surveys. There has
been much focus on the importance of field
methods and central assumptions of the
theory (see Buckland et al., 1993), but
little attention has been given to the
importance and influence of survey design.
Using data from the 1998 survey,
simulations were run to test the
relative efficiency of alternative
designs.
Key Researchers: Steve Dawson, Liz Slooten, Paul Wade, Will Rayment, Trudi Webster, Sam du Fresne
References:
Buckland, S.T., Anderson, D.R., Burnham, K.P. and Laake, J.L. Distance Sampling: Estimating Abundance of Biological Populations. Chapman and Hall, London. (1993)
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)
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., 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)
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