The abundance and distribution of bottlenosed dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand

Abstract

Photographic identification and standardized zigzag surveys were used to study the distribution and abundance of bottlenose dolphins in Doubtful Sound, New Zealand. Forty individuals were identified from nicks and markings on their dorsal fins. Chapman's and Bailey's modifications to the Lincoln–Petersen estimate and the computer program CAPTURE were used to estimate the number of marked individuals in the population, which ranged from 30 to 40 animals for three survey periods (two summers and a winter). The proportion of identifiable individuals in the population was assessed empirically as 65.5%. These data resulted in a total population estimate of approximately 58 individuals. The majority of the dolphins in the catalogue were found in each survey period, indicating their residency in the fiord. Movements of dolphins around the sound were not predictable, but there were areas in which dolphins were more likely to be found and other areas in which dolphins were never seen. However, there were no obvious seasonal or daily movement patterns.

Evidence for social role in a dolphin social network

“…The identity of individuals performing the behavioural events was defined either through direct visual observations or from either photographs or videos. The marking rate in this population is high (24,40) which means that practically all individuals can be recognised from marks on their dorsal fins. Therefore practically all the population (excluding calves) was equally likely to be recognised in this way, minimising sampling bias.…”

Epidermal diseases in bottlenose dolphins: impacts of natural and anthropogenic factors

“…Using this technique, levels of epidermal disease have been successfully documented in populations of wild bottlenose dolphins (Tursiops truncatus) o¡ north-east Scotland and Portugal (Thompson & Hammond 1992;Harzen & Brunnick 1997;Wilson et al 1997a). As bottlenose dolphins are distributed across a wide range of coastal habitats and are already studied using similar photographic techniques for other purposes (Wells 1991;Williams et al 1993) they o¡er an ideal opportunity for studying the relationships between environmental and anthropogenic conditions and the development of natural epidermal diseases.…”

Abundance and demography of bottlenose dolphins in Dusky Sound, New Zealand, inferred from dorsal fin photographs

“…e estimated abundance under two scenarios: (1) assuming all individuals in the population were marked (termed "Lp all marked"), and (2) using only individuals with dorsal fin nicks, and then scaling this estimate by a mark rate (termed "Lp nicked marked") consistent with previous studies of Fiordland bottlenose dolphins (williams et al 1993;Currey et al 2007). in each scenario, we considered the fieldwork conducted in early summer (November-December 2007) as the "capture" period, and the fieldwork conducted in late summer (February-March 2008) as the "recapture" period.…”

“…we identified calves by the presence of marks (primarily tooth rakes), the shape of their dorsal fins and continued association with the (presumed) mother whenever the mother was observed. Individuals were identified using photographs taken of either side of the dorsal fia To prevent errors arising from mismatching left and right sides, we estimated abundance using the left and right sides independently (wilson et al 1999), in addition to a combined estimate that assumed both sides could be matched (williams et al 1993;Currey et al 2007). …”

“…Of the three Fiordland populations, the Doubtful Sound population is the most accessible and has been extensively studied since 1990 (Williams et al 1993). The population shows adaptations to living in a cool water habitat, such as rotund body shape (Chong & Schneider 2001), seasonal calving (Haase & Schneider 2001), and seasonal changes in habitat use (Schneider 1999).…”