Occurrence, abundance, range, and residence patterns of Tursiops truncatus on the coast of Aragua, Venezuela

Abstract

Throughout the distribution of the bottlenose dolphin Tursiops truncatus, the occurrence, abundance, local distribution, and residential patterns are highly variable according to the pressure of the habitat where sighting occurs. In Venezuela, a study has been developed for the first time describing these aspects for the western of Aragua State (central coast of the country). From 2004 to 2008, 100 field surveys (30 km long) were conducted; the daily encounter ratio ranged from 0.79 to 1.11 dolphins/survey (Permanova, P < 0.01); the abundance was 18.70 (± 9.95) dolphins/transect (relative abundance of 0.62 dolphins/km), registering an increase since April 2007 by income of individuals (pseudo-t, P < 0.05). The sightings covered 56.63 km2, 90% of study area. Eighty-six dolphins were photo-identified (identification of new dolphins was constant). Residency analysis was limited to September 2006–August 2007 (continuous sampling); 7 (20.59%) residents (part of a group of 12), 9 (26.47%) occasional visitors (“neighboring group” and “outsiders”), and 18 (52.94%) transients were found. The study area is an open coast with shelter (bay) and prey that houses a resident group (sighted throughout the study) that was occasionally visited by a “neighbor” and occasional groups between October and February, and by transients throughout the year. This resident group inhabits the main bay and the coastal axis, and was associated (~ 75% of sightings) with Stenella frontalis (sighted throughout the year). We point out the importance of the area for both research and conservation due to the presence of dolphins throughout the year.