First estimate of common bottlenose dolphin (Tursiops truncatus) (Cetacea, Delphinidae) abundance off Uruguayan Atlantic coast

Abstract

The common bottlenose dolphin Tursiops truncatus is often observed throughout the oceanic coast of Uruguay. Historically, its distribution was wider, including the estuary of the Río de la Plata, but currently its occurrence seems to be restricted mainly to the Uruguayan Atlantic coast (Rocha Department). Conflicting interests and tradeoffs between conservation and development are being generated in Uruguay. On one hand, the establishment of protected areas, responsible tourism and sustainable fisheries are promoted, while on the other hand, foreign exploitation of natural resources and development of mega-infrastructure in coastal zone are facilitated. In this work, we provide the first estimate of bottlenose dolphin’s abundance along the Uruguayan Atlantic coast. These results can be used as baseline information for monitoring population trends and guiding conservation actions for bottlenose dolphins in Uruguay. Mark-recapture models were applied to data of photoidentified animals with long-lasting natural marks. Total population size estimates of 63 individuals (95% CI = 54–74) and 61 (95% CI = 53–73) were obtained from closed and open population models, respectively. Although the estimates are within the range of values obtained for other coastal bottlenose dolphin populations in the Southwest Atlantic Ocean, as well as other regions of the world, it is lower than the values reported for populations inhabiting open habitats. This small population is probably vulnerable to non-natural removals, environmental and demographic stochasticity. Therefore, precautionary actions are recommended given the planned development for this coastal region.