Distribution and abundance of Hector's dolphins off Otago, New Zealand

Abstract

Data on the distribution and abundance of Hector's dolphins (Cephalorhynchus hectori) along the Otago coastline, between Taieri Mouth and Ōamaru (approximately 130 km alongshore), were collected in 2010–2011. Alongshore surveys were conducted in small boats, travelling approximately 400 m from shore, at speeds of 10 to 15 knots. Photographic identification was used to establish sighting histories of identifiable individuals, and mark rate (36%, CV=12%, CI=28–45). Hector's dolphins were found in two areas: between Taiaroa Head and Cornish Head; and in the vicinity of Moeraki. Encounter records suggest there is little exchange between these zones. The Huggins closed capture method was used to estimate the number of marked individuals between Taiaroa Head and Cornish Head (approximately 22 km alongshore), and this value was scaled by mark rate to estimate a total population size of 42 individuals (CV=41%, CI=19–92). A closed population Bayesian analysis yielded a similar estimate of 37 individuals (CV=42%, CI=25–75).