Kate Grellier

Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises?

Most harbour porpoises found dead on the north–east coast of Scotland show signs of attack by sympatric bottlenose dolphins, but the reason(s) for these violent interactions remains unclear. Post–mortem examinations of stranded bottlenose dolphins indicate that five out of eight young calves from this same area were also killed by bottlenose dolphins. These data, together with direct observations of an aggressive interaction between an adult bottlenose dolphin and a dead bottlenose dolphin calf, provide strong evidence for infanticide in this population. The similarity in the size range of harbour porpoises and dolphin calves that showed signs of attack by bottlenose dolphins suggests that previously reported interspecific interactions could be related to this infanticidal behaviour. These findings appear to provide the first evidence of infanticide in cetaceans (whales, dolphins and porpoises). We suggest that infanticide must be considered as a factor shaping sociality in this and other species of cetaceans, and may have serious consequences for the viability of small populations.

Considering the temporal when managing the spatial: a population range expansion impacts protected areas-based management for bottlenose dolphins

Management of marine species has increasingly focused on key site protection. Initiatives to protect bottlenose dolphins, Tursiops truncatus, under the EU Habitats Directive reflect this trend. The boundaries of the Moray Firth candidate Special Area of Conservation (cSAC) were intended to include the main Scottish population’s core range, following research conducted in the 1980s and early 1990s. However, during implementation, anecdotal sightings increased outside the cSAC. Here, the authors examine existing datasets to identify whether these reports reflect simply elevated awareness among public observers or real changes in distribution. Dolphins photo-identified in areas originally considered to be outside the population’s range confirmed they originated from the protected population. These individuals became rarer within the cSAC during the 1990s. Scottish bottlenose dolphins kill harbour porpoises, Phocoena phocoena, and carcasses from these interactions also became more frequent outside the cSAC during the 1990s. These results indicate mobility of this ‘resident’ dolphin population on a timescale similar to that of the implementation of the European Directive designed to protect it. Consequently, this and other similar designations, may afford less protection than originally envisioned and the authors recommend, therefore, that the potential for long-term mobility should be actively incorporated into such management structures from the outset.

Bottlenose dolphins using the Sound of Barra, Scotland

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.