Bottlenose Dolphin (<I>Tursiops truncatus</I>) Abundance, Site Fidelity, and Group Dynamics in the Marlborough Sounds, New Zealand

Abstract

Bottlenose dolphins (Tursiops truncatus) are consistently observed in the Marlborough Sounds, New Zealand. However, prior to the present study, no research has previously focused on this species within these waters, despite the potential for human impacts. Photo-identification undertaken during boat-based surveys conducted between 2003 and 2005 were used to assess occurrence, abundance, and movement patterns of bottlenose dolphins in the Marlborough Sounds. Longterm site fidelity was evident, with the majority of individuals resighted over multiple years. Lagged identification rates showed consistency over a 4-y period, with some individuals remaining for longer periods, while others frequently interchanged between different areas of the Marlborough Sounds. Migration rates were high, with approximately 25% leaving and entering the 890 km2 region annually. Bottlenose dolphins in the Marlborough Sounds appear to form part of a larger, open, coastal population consisting of 385 individuals, with 211 (95% CI = 195 to 232) dolphins utilizing the region per annum. While their occurrence within these waters is frequent, the Marlborough Sounds appear to be only a section of a much larger home range for this bottlenose dolphin population.