Residency patterns of Bottlenose dolphins (Tursiops truncatus) in south west Portugal

Although the presence of bottlenose dolphins has already been documented in Portugal, there is very little known about these animals occurring along the coast. The study aimed at creating the first photo-ID catalogue of bottlenose dolphins for Sagres area (SW Portugal), investigating their residency patterns, identifying hotspots for their occurrence, and analysing groups composition and behaviour. Analysis of photographs taken on-board opportunistic platforms between years 2007-2013 resulted in identification of 173 individual dolphins with unique markings, what led to construction of a photo-identification catalogue and allowed for investigation of residency patterns. There were no resident animals found in this area. 34% dolphins were classified as semi-resident. The remaining 66% of the identified animals, seen only once, were classified as non-resident. For over 70% of the semi-resident animals, temporal range of sightings was shorter than one year, indicating that most of bottlenose dolphins were sighted while passing by Sagres waters and only few of them re-emigrated to the study area. Analysis of the groups sizes shows, that groups up to 20 animals were the most common. The encountered groups varied in composition and behaviour, however feeding behaviour was clearly prevailing. Finally, hotspots for bottlenose dolphins observations were found along 200m isobath.

ISCED Categories

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0521 - Ecology