A review on the distribution, abundance, residency, survival and population structure of coastal bottlenose dolphins in Argentina

Abstract

Although bottlenose dolphins Tursiops truncatus are among the most common delphinid species, global population trends remain poorly understood. To improve the knowledge of the species in the Southwest Atlantic Ocean, this paper reviews all available data related to the distribution and occurrence, abundance, residency and ranging patterns, group size and composition, survival and reproduction and population structure of the coastal bottlenose dolphin in Argentina. Most information proved to be scattered in time and space. Based on the available data, total abundance of coastal bottlenose dolphins in Argentina appears to be low. Data show sightings decreased notably since the 1990s in the northern province of Buenos Aires and the province of Chubut, with the species having disappeared completely from the former region. Data also indicated that two genetically and morphologically distinct coastal populations occur in Argentinean coastal waters, with a sympatric distribution in the provinces of Rio Negro and Chubut. One is an isolated ‘Evolutionary Signifcant Unit’ within the larger Southwest Atlantic, whereas the other population appears to be genetically related to the Southwest Atlantic offshore ecotype.  In the absence of more substantial data, the present information is pertinent to our scientifc knowledge of the species in the country, collating all published information as well as information from grey literature and previously unpublished data. However, the available information appears to remain insufcient to explain the apparent decline in sightings and to assess the remaining abundance nationwide accurately. Therefore, we strongly recommend increased research efforts for an in-depth assessment of the species’ population status in Argentina.