Near‐shore distribution and abundance of dolphins along the West Coast of the South Island, New Zealand

New Zealand Journal of Marine and Freshwater Research - N Z J MAR FRESHWATER RES 01/1998; 32(1):105-112. DOI: 10.1080/00288330.1998.9516809

ABSTRACT Compared to other stretches of the New Zealand coast, very little is known about the cetacean fauna off the West Coast of the South Island. The purpose of this paper is to describe the near‐shore distribution and abundance of dolphins in that area by summarising the results of two major studies. Between February 1995 and February 1997, 97 day trips were undertaken from Westport, Greymouth, and Jackson Bay in a small boat to survey the near‐shore distribution of dolphins. Between July 1994 and February 1997, 283 field days were spent on the water in Doubtful Sound studying the local bottlenose dolphin (Tursiops truncatus) population of c. 63 individuals. At the same time, three longer surveys were undertaken into other fiords of Fiordland which indicated the presence of further populations. Altogether, five delphinid species were recorded in various abundances. Small‐medium‐sized groups of Hector's dolphins (Cephalorhynchus hectori) with 1–60 individuals were observed in almost all areas of Westland in winter as well as in summer. Maximum densities peaked at 5–18 individuals per nautical mile of coastline between Cape Foulwind and Hokitika. Dusky and common dolphins (Lagenorhynchus obscurus and Delphinus delphis) occurred almost exclusively in summer in groups of 2–150 individuals, often with calves, especially at Cape Foulwind and Jackson Head. Bottlenose dolphins (Tursiops truncatus) and killer whales (Orcinus orca) were observed rarely off Westland, but occurred more frequently in Fiordland.

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    ABSTRACT: 1.The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture-recapture models.2.The most parsimonious model for adults provided a time-invariant, sex-invariant estimate of survival (ϕa(1990–2008)=0.9374; 95% CI: 0.9170–0.9530), marginally lower than prior estimates for wild bottlenose dolphins.3.The most parsimonious model for calves indicated a significant time-variant decline in survival from an estimate similar to other populations (ϕc(1994–2001)=0.8621; 95% CI: 0.6851–0.9473) to a current estimate that is, to our knowledge, the lowest recorded for free-ranging bottlenose dolphins (ϕc(2002–2008)=0.3750; 95% CI: 0.2080–0.5782).4.Information theoretic evidence ratios suggested that observed patterns in calf survival were 22 times more likely to be explained by a decline coincident with the opening of a second tailrace tunnel for a hydroelectric power station than by a decline in any other year or across multiple years.5.Projections using an age-structured stochastic population model indicated that the current level of calf survival was unsustainable (population decline: 100% of model runs; population extinction: 41.5% of model runs) and was a key factor in the observed population decline in Doubtful Sound. Copyright © 2008 John Wiley & Sons, Ltd.
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