Line-transect survey of Hector's dolphin abundance between Motunau and Timaru

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Summary

Methods and results of the first boat-based line-transect survey in New Zealand waters are reported. The survey was designed to quantify Hector's dolphin (Cephalorhynchus hectori) abundance between Motunau and Timaru, East Coast, South Island, out to 4 nautical miles from shore. Greatest dolphin densities were found in Akaroa Harbour, along Birdings Flat (between Banks Peninsula and the Rakaia River) and off the eastern side of Banks Peninsula.

Analyses suggest that overall abundance in the survey area is around 2400 animals (CV=22%). A preponderance of dolphin sightings in which orientation was towards the vessel indicates attraction to the vessel, at least within a radial distance of 400 m. This would lead to an overestimate of abundance. Quantifying the effect of attraction on abundance estimates should be an important objective of further survey work on this species.