Bottlenose dolphins using the Sound of Barra, Scotland

Abstract: Though widely reported around the European Atlantic coast, details relating to the overall distribution and site fidelity of bottlenose dolphins (Tursiops truncatus) in these waters remains poorly documented. Studies in areas where the majority of sightings occur have found evidence of seasonal, or year round, residency and social interaction among sympatric individuals. However, the degree of individual and genetic mixing between these studied communities, and their relevance to true biological populations, remains largely unknown. To better understand the wide-scale population structure of bottlenose dolphins off Western Europe, these lesser-known concentrations also need to be investigated. In this study, we examined one such area off the west coast of Scotland where bottlenose dolphins have been repeatedly sighted. The Sound of Barra is a shallow passage between two of a chain of islands, the Outer Hebrides, that run roughly north-south 50 to 70 km west of the Scottish mainland. Boat based surveys were carried out in the Sound in September 1995 and June 1998. Bottlenose dolphins were found during both survey periods. Repeat identifications of the same individuals in both years suggested that animals are site faithful. Application of photo-identification data to a two-sample Petersen mark-recapture analysis suggested that this community is small, at between six to 15 individuals. The results of this study enhance knowledge of bottlenose dolphin distribution and site fidelity off western Europe and we suggest that there is little, if any, regular interchange of individuals occurring between the Barra group and its nearest known neighbouring large community off eastern Scotland. The relative importance and long-term viability of small clusters of animals, such as those in the Sound of Barra, compared to the larger, better known, communities remains to be established.


Document Type: Research article

Pages: 378-382

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