Structure and abundance of bottlenose dolphins (Tursiops truncatus) in coastal Setúbal Bay, Portugal

The environmental plasticity of bottlenose dolphins leads to a range of inter-specific variations in ecological parameters that make worldwide generalizations difficult. Thus, regional studies about bottlenose dolphins are important to the overall conservation of this species. The aim of this study was to characterize for the first time bottlenose dolphins that occur in the coastal regions of Setúbal (Portugal) using two temporally distinct datasets: dataset 1 (1998–2001) and those in dataset 2 (2007–2011). Bottlenose dolphins identified in dataset 1 were considered a closed and a more cohesive group than dataset 2, with stable associations and an abundance of 106 (95% CI = 69–192) individuals. Dataset 2 seemed to be composed of an open group of 108 (95% CI = 83–177) animals, with a migration rate of 19% (SE = 0.1) individuals per year, and with low association values. The proportion of ‘regulars’ (dataset 1, 22%; dataset 2, 12%), ‘frequent’ (dataset 1, 10%; dataset 2, 14%) and ‘occasional’ (dataset 1, 68%; dataset 2, 73%) animals was relatively similar between datasets. In addition, there was no matching of individuals between datasets which could be related to large-scale movements of the individuals and/or the carrying capacity of the study area.