Predator movements in complex geography
: Spatial distribution and temporal occurrence of low-density bottlenose dolphin communities off western Scotland

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by OU/Aberdeen)


Scotland is increasingly focussing on sustainable energy sources, and several marine renewable projects for offshore wind, wave and tidal installations have been proposed for Scottish waters, including off western Scotland. The realisation of these developments has the potential to negatively impact local marine species, including marine mammals. The west coast of Scotland is inhabited by two small under-studied common bottlenose dolphin (Tursiops truncatus) communities: the Inner Hebrides and the Sound of Barra (SoB) community. To allow assessments of anthropogenic impacts on these dolphins and development of efficient management to mitigate against these, an increased understanding of their general distribution patterns, residency, and spatial and temporal mobility is required. Therefore, using a variety of research methods (dedicated cetacean surveys and targeted photo-ID trips, acoustic monitoring and the collection of opportunistic photo-ID and sightings data), this study examined local dolphin mobility patterns by investigation of their spatial distribution and temporal occurrence.
The results provided evidence for a prolonged (at least 2006-2013) social and geographic isolation between both dolphin communities. Dedicated cetacean surveys (HWDT 2003-2012) demonstrated that dolphins of the Inner Hebrides community were mainly found in nearshore waters. Dedicated and opportunistic photo-ID (2000-2014) and sightings data (1989-2014) revealed that these dolphins were present year-round and that individuals ranged widely throughout the entire currently known communal range. Several dolphins demonstrated long-term fidelity to the region and were identified over at least eight years. Combined, the year-round presence of individual dolphins and their long-term site-fidelity indicates a resident community. New individuals were identified throughout the study, but these were typically only sporadically photographed. This suggests there is the potential for the presence of other vagrant or more cryptic individuals. Various calves were identified and included calves of both known and unknown females.
In contrast, although based on limited data, dolphins from the SoB community appeared to occupy a restricted range and were, with the exception of one female, never photographed away from the southern Outer Hebrides (i.e. near Barra and the Uists).

Summer photo-ID data (1995-2013) revealed an annual community size of ≤15 individuals, and the long-term summer presence of these dolphins with four dolphins first identified in 1995 still present in 2013. Acoustic C-POD monitoring in the area detected dolphin presence year-round, although echolocation occurrence varied through the year, and the tidal and diel cycles. The long-term individual fidelity and year-round acoustic detections collectively support the presence of a resident community. This community appears female-dominated, and at least eight calves were being born into the community since 2006, yet no other new individuals were identified. Although limited in available data, the population’s demographic parameters (birth rate, calving interval and calf survival) were comparable to those reported for the species globally.
This study showed that the integration of complementary methodological approaches is useful in investigating mobility patterns of low-density populations. Moreover, this study included two more alternative approaches: acoustic monitoring in natural geographic bottlenecks and the collection of opportunistic sightings and photo-ID data which included pro-active searches via social media. Whereas both methods revealed limitations and biases, they both demonstrated opportunities for further development.
Despite the year-round presence, acoustic detections and sightings during the winter were limited and the occurrence and distribution of dolphins from both communities during this period remains unclear, as is the demographic connection between the communities and with neighbouring communities/populations in UK and Irish coastal and offshore waters. As such, continued photo-ID and further genetic studies are required to monitor abundance trends, demographic parameters and winter presence, assess population structure and connectivity, and hence assessment of the viability of these small resident communities. In any case, the results presented herein support that these communities be managed as separate conservation units.
Date of Award2 Jun 2016
Original languageEnglish
Awarding Institution
  • University of Edinburgh
SponsorsMASTS Scotland & Harper Mcleod LLP
SupervisorBen Wilson (Supervisor) & Gordon Hastie (Supervisor)

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