SOCIAL STRUCTURE OF LAHILLE’S BOTTLENOSE DOLPHIN Tursiops truncatus gephyreus (CETACEA: DELPHINIDAE) OFF THE URUGUAYAN MARINE COAST

"Information about the social relations among individuals is essential to define and develop management plans for a socially structured population. Association data for 25 adult Lahille’s bottlenose dolphins were obtained from 189 photo-identification surveys that took place between January 2007 and May 2009 in La Coronilla-Cerro Verde and Cabo Polonio, Rocha, Uruguay. Group size averaged 5.22 individuals (SD= 3.77, n= 255). Coefficients of association were calculated using the Half-Weight Index. Most of the associations were weak (79.7%) and variation of real association indices was greater than would be expected by chance. Thus, the null hypothesis that individuals associated randomly was rejected. Standardized Lagged Association Rate analysis also indicated that nonrandom associations between individuals persisted over the study period. The exponential decay model that fits best to the data suggested the existence of constant companions and casual acquaintances. This study is the first report about the social structure of the population of Lahille’s bottlenose dolphin inhabiting the Uruguayan marine coasts. Cerro Verde and Cabo Polonio were the first marine protected areas selected by the government of Uruguay. However, information about the ecology and behavior of the species in these areas is still insufficient. It is recommended that the results of this study be taken as baseline information to assess the conservation status of this population, as well as for the development of adequate conservation and management plans."