June 13, 2024

A Long-Term Opportunistic Photo-Identification Study of Bottlenose Dolphins (Tursiops truncatus) off Aberdeen, United Kingdom: Conservation Value and Limitations


Caroline R. Weir, Sarah Canning, Kevin Hepworth, Ian Sim, and Karen A Stockin


Abstract: The waters of the Inner Moray Firth were designated a Special Area of Conservation (SAC) in 2005 for the conservation of the bottlenose dolphin (Tursiops truncatus) in northeast Scotland. However, the long-term conservation of this population requires monitoring throughout its entire known range. Opportunistic photo-identification of bottlenose dolphins occurred during 65 cetacean surveys conducted between 1999 and 2008 in the coastal waters of Aberdeenshire. A total of 88 bottlenose dolphin photo-identification encounters resulted in one to 45 animals identified per survey. The minimum annual total population size based on marked animals alone was 62 individuals, and the discovery curve indicated that the population has not yet been adequately sampled. Of 40 highly distinctive adult animals, the annual sighting rate ranged from 0.167 (seen in one year only) to 1.000 (seen every year). The cumulative monthly sighting rate varied from 0.091 (photographed in one month only) to 0.636 (photographed during seven of the 11 combined survey months in the 2001 to 2008 study period). The overall seasonal occurrence of dolphins off Aberdeenshire peaked during May and June, when 65% of distinctively marked animals were recorded per month (combined data for 2001 to 2008). Eighty-four percent of distinctively marked dolphins were matched with those photographed in the Inner Moray Firth, while 93% were matched with those photographed in the southern Outer Moray Firth. Despite its opportunistic nature, the photo-identification study provided valuable information on a population of bottlenose dolphins in a poorly studied part of their range. The high percentage of matches with dolphins from the Moray Firth SAC indicates that over half of the known northeast Scotland population uses the Aberdeenshire region, and some individuals do so regularly. The frequent occurrence off Aberdeen of bottlenose dolphins from a protected SAC has repercussions for the conservation and management of the population and for the effectiveness of the SAC for their longterm protection.

Key Words: photo-identification, population size, distribution, marine protected area (MPA), Aberdeen, bottlenose dolphin, Tursiops truncatus

Document Type: Research article

DOI: 10.1578/AM.34.4.2008.436

Page Numbers: 436-447

Info SKU: Vol__34__Iss__4__Weir_et__al_ Category: