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Foley A.,Mayo Institute of Technology, Galway | McGrath D.,Mayo Institute of Technology, Galway | Berrow S.,Shannon Dolphin and Wildlife Foundation | Gerritsen H.,Marine Institute of Ireland
Aquatic Mammals | Year: 2010

The Shannon Estuary is home to Ireland's only known resident population of bottlenose dolphins (Tursiops truncatus) and is designated as a candidate Special Area of Conservation (cSAC) for this species. Proper conservation management of these dolphins requires an understanding of the social structure of this population. Four years of photoidentification data (2005 to 2009, excluding 2007) were used to construct sociograms that complement a cluster analysis of individually marked dolphins and their associates. The results found little evidence of social stability or group fidelity for this study's dolphin population. Analysis of dolphins observed in consecutive years showed that the probability of group members encountering an individual dolphin in the second year did not depart from a random model. The social parameters for this resident population seem to be typical for this species. Bottlenose dolphins are found to exhibit a highly fluid, dynamic social structure within which individuals change their composition and associates regularly. These dolphins in the Shannon Estuary appear to live in a fission-fusion based society.

Robinson K.P.,Cetacean Research and Rescue Unit | O'Brien J.M.,Mayo Institute of Technology, Galway | Berrowi S.D.,Shannon Dolphin and Wildlife Foundation | Berrowi S.D.,Irish Whale and Dolphin Group | And 12 more authors.
Journal of Cetacean Research and Management | Year: 2012

The potential for long distance movements in common bottlenose dolphins (Tursiops truncatus) from six UK and Irish study sites was examined using photographs of natural markings. Here we provide the first evidence for long-term re-sightings between the Moray Firth, Inner Hebrides and across international borders to the Republic of Ireland as determined for eight individuals over a ten year period from 2001 to 2010. Minimum dispersal distances of up to 1,277km were resolved providing a new distance record for the species in European waters. Although none of the sightings were made within protected areas, several were made in waters used by animals from a Special Area of Conservation (SAC) revealing some evidence for connectivity between areas previously regarded as discrete. Our findings highlight the need to mitigate broader-scale anthropogenic impacts affecting these dolphins across multiple sites throughout their coastal range. Accordingly, we underline the importance of developing wider conservation measures for this species in UK and Irish waters, but particularly in prospective corridor areas potentially linking designated SACs in the Moray Firth, Cardigan Bay and Shannon Estuary.

Berrow S.,Shannon Dolphin and Wildlife Foundation | Berrow S.,Mayo Institute of Technology, Galway | O'Brien J.,Mayo Institute of Technology, Galway | Groth L.,Mayo Institute of Technology, Galway | And 2 more authors.
Aquatic Mammals | Year: 2012

An abundance assessment of bottlenose dolphins (Tursiops truncatus) in the Lower River Shannon candidate Special Area of Conservation (cSAC) was undertaken between July and October 2010 using photo-identification. European Union Member States are obliged to designate SACs for bottlenose dolphins to protect important habitats. The Lower River Shannon is the only cSAC in Ireland for this species. A cumulative total of 273 bottlenose dolphins were photographed during the 12 transects, and from these a total of 116 individual animals were identified. They were categorized as follows: 71 with Severity Grade 1 marks, 21 with Severity Grade 2 marks, and 24 with Severity Grade 3 marks. There were 50 dolphins with permanent marks (Severity Grade 1) recorded on both sides of the dorsal fin, 64 on the left hand side only, and 57 on the right hand side only. There was an overlap, with some dolphins occurring in more than one category. Estimates of abundance were calculated using left side, right side, and both side identifications. The proportion of dolphins with re-identifiable marks (Severity Grade 1 only) ranged from 0.60 to 0.63. The estimated abundance of marked individuals was elevated depending on the estimated proportion of marked individuals in the population to give a final estimate of 107 ± 12, CV = 0.12 (95% CI = 83 to 131). Previous abundance estimates for bottlenose dolphins in the Lower River Shannon cSAC ranged from 114 in 2008 to 140 in 2006; the present estimate was within this range and also within the 95% Confidence Intervals for all surveys carried out to date. This suggests that, within the power of the survey technique, the population of bottlenose dolphins in the Lower River Shannon cSAC is relatively stable.

Mirimin L.,University College Cork | Mirimin L.,National University of Ireland | Miller R.,University College Cork | Dillane E.,University College Cork | And 5 more authors.
Animal Conservation | Year: 2011

The identification of localized discrete populations is particularly important to the management and conservation of animal species, especially in the marine environment, where potential for dispersal is high but barriers to gene flow are often not clear. We investigated population genetic structuring of bottlenose dolphins Tursiops truncatus found along the west coast of Ireland, with particular attention to the Shannon Estuary, which is the only candidate Special Area of Conservation designated for this species in Irish waters. A genetic structure analysis using 62 biopsy samples from free ranging dolphins and 23 necropsies from stranded dolphins revealed fine-scale population structure among three distinct populations. The Shannon Estuary population appears to be genetically isolated from adjacent coastal areas, with the exception of four animals sampled from a small group of six dolphins that are now resident in Cork Harbour (south coast) indicating ongoing gene flow or recent dispersal between these two areas. A second genetically distinct aggregation was identified in the Connemara-Mayo region, where recent photo-identification studies have suggested that dolphins found in this area show a degree of site fidelity. We found moderate nuclear (15 microsatellites) and low mitochondrial (544bp of the control region) gene diversity in dolphins using the Shannon Estuary and the Connemara-Mayo region, while dolphins that stranded along the coast showed markedly higher levels of gene diversity at both classes of markers. Specifically, these stranded dolphins formed a third genetically distinct cluster, which may be part of a larger pelagic population, as also suggested by the high levels of gene diversity. These results provide new insights into population structure of bottlenose dolphins in Irish waters and will aid future management and conservation of the species in the eastern North Atlantic. © 2011 The Authors. Animal Conservation © 2011 The Zoological Society of London.

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