| Summary: | Understanding the abundance, ranging patterns and the degree of isolation of populations are key concepts towards successful conservation measures. For my PhD thesis I applied a multi-disciplinary approach that encompassed genetic, mark-recapture and acoustic analyses to identify fine-scale population structure, residency, ranging patterns, habitat use and abundance of bottlenose dolphins, Tursiops truncatus, in Irish waters. Whole mitochondrial genome sequencing together with the latest phylogeographic tools revealed the complex evolutionary and demographic history of bottlenose dolphins in the wider North-east Atlantic highlighting the influence of past climate change following the end of the last glaciation on the current population structure. By analyzing photo-identification and genetic data together, I provided the first evidence for the near complete social isolation of two adjacent coastal populations, likely driven by a combination of socioecological factors. For the first time, the ongoing genetic dispersal between the populations was quantified, and it was established that the populations are effectively genetically isolated and should be managed separately. A precise abundance estimate of 189 (CV = 0.11), derived for one of the coastal populations using a new robust Bayesian modelling framework, together with results from passive acoustic monitoring on site occupancy, can be used to guide monitoring designs in Ireland and possibly elsewhere. The effect of varying levels of sampling effort on the minimum detectable decrease in population size were also examined, and it was found that in order to detect an overall decline of 25% in abundance (guideline in the EU’s Habitats Directive), the coefficient of variation (CV) around the estimate would have to be as low as 0.08 for a six-year reporting period. This would be difficult, if not impossible, to achieve for such a mobile population. An alternative strategy, where the 25% decline could be detected, would be to sample the abundance every two years.
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