Bottlenose dolphins at the southern extreme of the south-western Atlantic: local population decline?

Abstract

The management scheme of Marine Protected Areas (MPAs) includes monitoring protocols but such activities are not always carried out. This is the case for Golfo San Jose ´, a MPA in northern Patagonia, Argentina. It was created in 1975 for the protection of the southern right whale (Eubalaena australis) breeding grounds. Other components of the system, such as dolphin populations have received little attention. This study is the first attempt to estimate sighting rates, group size and overall abundance of a bottlenose dolphin (Tursiops truncatus) population in Golfo San Jose and adjacent areas after 30 years. An analysis of the seasonal sighting rates indicates that bottlenose dolphins were present in the study area throughout the year but a decline in group size and abundance and major shift in distribution was detected when compared with previous published reports. The settlement of the MPA failed to secure the persistence of the bottlenose dolphin population within its boundaries. Possible explanations for the detected decline are addressed including increased natural mortality, human induced mortality and disturbance, resources depletion and environmental shift.