The Social Structure of Free-Ranging Bottlenose Dolphins

Wells, Randall S.; Scott, Michael; Irvine, A. Blair

doi:10.1007/978-1-4757-9909-5_7

Cited by 453 publications

(652 citation statements)

References 29 publications

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“…When dolphins were sighted, the observer(s) attempted to take good-quality images of every dolphin dorsal fin in the group. A dolphin group was defined as all dolphins within a 100-m radius of any other dolphin that was involved in similar behavioural activities (Irvine et al 1981;Wells et al 1987;Parra et al 2006;Fury and Harrison 2008). Data for each group on species identification, location and time of day, group size and behaviour were recorded on a hand-held Personal Digital Assistant using Cybertracker software (www.…”

Section: Field Methodsmentioning

confidence: 99%

Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

et al. 2014

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Abstract, and grey shading in the table). The errors were due to transcription error and in no way affect the outcome and conclusions of the study. AbstractKey results. Abundance estimates for the three species varied across the sampling periods, with the estimated number of Australian snubfin dolphins ranging from 136 (s.e. 62) to 222 (s.e. 48); from 48 (s.e. 17) to 207 (s.e. 65) for the Australian humpback dolphin; and 34 (s.e. 16) to 75 (s.e. 26) for the bottlenose dolphin. AbstractContext. Three dolphin species occur in coastal waters of monsoonal northern Australia: the Australian snubfin (Orcaella heinsohni), humpback (Sousa sp.) and the bottlenose (Tursiops sp.). Their overall population size and trends are poorly known, and their conservation status has been difficult to resolve, but can be expected to deteriorate with likely increased development pressures.Aims. We sought to provide an estimate of abundance, and apparent survival, of the three dolphin species at the largely undeveloped harbour of Port Essington (325 km 2 ), Northern Territory, with repeated sampling over a 2.9-year period. Given increasing obligations to undertake population assessments for impact studies at proposed development sites, we assess the strengths and limitations of a systematic sampling program.Methods. We used photo-identification data collected during systematic boat-based transect surveys undertaken from 2008 to 2010 and Pollock's robust capture-recapture design model. Key results. Total abundance estimates for the three species were variable across different sampling periods. The estimated number of individuals in the sampled area varied per sampling episode from 136 (s.e. 62) to 222 (s.e. 48) for snubfin, from 48 (s.e. 7) to 207 (s.e. 14) for humpbacks and from 34 (s.e. 6) to 75 (s.e. 9) for bottlenose dolphins. Apparent survival was estimated for snubfin at 0.81 (s.e. 0.11), humpbacks at 0.59 (s.e. 0.12) and bottlenose at 0.51 (s.e. 0.17) per annum.Key conclusions.(1) The values derived here provide some of the only estimates of local population size for these species across monsoonal northern Australia; (2) population-size estimates varied considerably among seasons or sampling episodes; (3) the low apparent survival probabilities indicated that many individuals may move at scales larger than the study area; (4) density of snubfin and humpback dolphins in the present study area exceeded the few other estimates available for these species elsewhere in Australia.Implications. The present study provided the first baseline estimates of abundance and apparent survival for three coastal dolphin species in monsoonal northern Australia. Such information is becoming increasingly important as development pressures intensify in coastal areas. Sampling protocols for future monitoring and impact assessment need an enhanced consideration of seasonality and scale issues.

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Section: Field Methodsmentioning

confidence: 99%

Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

et al. 2014

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“…In Sarasota Bay, Florida, adult males form stable pairs, but trios and second-order alliances are not in evidence ( Wells et al 1987;Connor et al 2000;Wells 2003). Greater sexual size dimorphism, a less malebiased operational sex ratio or fewer sharks could explain the lack of trios , but the population density and thus overall encounter rates between males may be much higher in Shark Bay, favouring larger and more levels of alliances .…”

Section: The Ecology Of Alliance Formation (A) First-order Alliance Sizementioning

confidence: 99%

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Connor

2007

Phil. Trans. R. Soc. B

231

229

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Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

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“…In the context of the fluid, fissionefusion society of coastal bottlenose dolphins (e.g. Wells et al 1987;Smolker et al 1992), changes to grouping behaviour in response to vessels might be considered unimportant. We suggest that disruption of grouping behaviour, no matter how short term, may have far-reaching repercussions for species such as bottlenose dolphins that rely on longterm, individually specific bonds (e.g.…”

Section: Article In Pressmentioning

confidence: 99%

Interpreting short-term behavioural responses to disturbance within a longitudinal perspective

et al. 2006

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We documented immediate, behavioural responses of Indo-Pacific bottlenose dolphins (Tursiops sp.) to experimental vessel approaches in regions of high and low vessel traffic in Shark Bay, Western Australia. Experimental vessel approaches elicited significant changes in the behaviour of targeted dolphins when compared with their behaviour before and after approaches. During approaches, focal dolphin groups became more compact, had higher rates of change in membership and had more erratic speeds and directions of travel. Dolphins in the region of low vessel traffic (control site) had stronger and longer-lasting responses than did dolphins in the region of high vessel traffic (impact site). In the absence of additional information, the moderated behavioural responses of impact-site dolphins probably would be interpreted to mean that long-term vessel activity within a region of tourism had no detrimental effect on resident dolphins. However, another study showed that dolphin-watching tourism in Shark Bay has contributed to a long-term decline in dolphin abundance within the impact site (Bejder et al., in press, Conservation Biology). Those findings suggest that we documented moderated responses not because impact-site dolphins had become habituated to vessels but because those individuals that were sensitive to vessel disturbance left the region before our study began. This reinterpretation of our findings led us to question the traditional premise that short-term behavioural responses are sufficient indicators of impacts of anthropogenic disturbance on wildlife.

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The Social Structure of Free-Ranging Bottlenose Dolphins

Cited by 453 publications

References 29 publications

Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Interpreting short-term behavioural responses to disturbance within a longitudinal perspective

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