Abundance, residency, and habitat utilisation of Hector's dolphins (Cephalorhynchus hectori) in Porpoise Bay, New Zealand

Abstract

Theodolite tracking and boat‐based photo‐identification surveys were carried out in the austral summers of 1995/96 and 1996/97 to assess abundance, residency, and habitat utilisation of Hector's dolphins (Cephalorhynchus hectori van Beneden 1881) in Porpoise Bay, on the south‐east corner of the South Island of New Zealand. Data are consistent with the model of a small resident population that is visited occasionally by members of neighbouring populations. Mark‐recapture analysis of photographically identified individuals, along with data on the proportion of animals bearing identifying marks, indicates a local population of 48 dolphins (95% CI = 44–55) in 1996/97. Dolphins spent a large proportion of their time in a small area inside the bay. Dolphin sightings were more congregated in successive time periods from early morning to late afternoon. No pattern of diurnal movement into and out of the bay was observed.