Abstract
The bottlenose dolphins found in the Moray Firth Special Area of Conservation (Moray Firth SAC) are part of a Scottish east coast population of approximately 200 animals that ranges south past Aberdeen to the Firths of Tay and Forth. In the United Kingdom, bottlenose dolphins are protected nationally and internationally, which may need to be considered during impact assessments for marine development and exploration. Before robust impact assessments can be completed, information on species distribution, abundance and population parameters are needed to understand the potential type and magnitude of effects.
Analysis of the photo-identification data collected since 1989 within and outside the Moray Firth SAC estimate an annual probability of apparent survival (0.947 SE=0.005) similar to estimates previously reported for this population, as well as a low probability of dolphins temporarily emigrating outside the study area, consistent with this being a highly resident population. Analysis of detailed information on the calving histories of reproductive females in the study population estimate a mean inter-birth interval of 4.49 years (95% CI 3.94 to 4.93 years) equivalent to an annual fecundity rate of 0.22 (95% CI = 0.22 to 0.25).
More consistent data have been collected outside the Moray Firth since 1997, primarily in the Tayside and Fife area. Sighting histories of individual animals have been constructed using photo identification of long-lasting natural marks. Individuals are known to range up and down the coast, but there is much spatial and temporal variability in individual movements. Across all years of data, females show a significantly (p=0.0497) higher probability of presence within the Moray Firth SAC than males, and males appear to move between areas more frequently than females. In the Tayside and Fife area dolphins were encountered more often in and around the Tay estuary in waters less than 20 m deep and within 2 km of the coast. The Tay estuary has consistently high encounter rates of bottlenose dolphins over the years. Between 71 (95% CI 63-81) and 91 (95% CI 82-100) bottlenose dolphins from the east coast population were estimated to be using the Tay area during 2009-2013, representing approximately 35-46% of the total Scottish east coast population. In the Tayside and Fife area, a minimum of seven dedicated photo-identification trips, spread over three months, are required to obtain an estimate of abundance with acceptable consistency and precision.
Bottlenose dolphins were also frequently encountered along the coast between Montrose and Aberdeen in waters less than 20 m deep and within 2 km of the coast. Dolphins were frequently found at the entrance to Aberdeen Harbour and adjacent waters. Data collected in 2012-13 indicate that around 25% of the total Scottish east coast population uses the area between Stonehaven and Aberdeen. Based on these recent data, 118 (95% CI: 98-143) and 119 (95% CI: 101-140) individuals were estimated to be using the area between Aberdeen and the Firth of Forth in 2012 and 2013, respectively, representing greater than 60% of the total Scottish east coast bottlenose dolphin population.