BIOGEOGRAPHY OF COMMON DOLPHINS (GENUS DELPHINUS) IN THE SOUTHWESTERN ATLANTIC OCEAN

TAVARES, M; MORENO BENITES I; SICILIANO, S; RODRÍGUEZ, D; SANTOS, MCO; LAILSON BRITO JR, J; FABIÁN, ME

Mendoza, Argentina

Congreso; X Congreso Internacional de Mastozoología; 2009

SAREM

The common dolphins (genus Delphinus Linnaeus, 1758) present one of most complex taxonomy and distributional patterns among all cetaceans. Although the taxonomy and the distribution seem to have been clarified in the eastern North Pacific and partially in Indo-Pacific Oceans, these questions are still unclear in the Southwestern Atlantic Ocean (SWA). We reviewed data from strandings, incidental catches and sightings since 1922, compiling 184 records. Systematic surveys were conducted in five major areas. Twenty one natural history collections were examined, with 135 skulls analyzed. Common dolphins seem to occur in three potential stocks in the SWA: a small and tentatively isolated in northern Brazil and two others from southeastern Brazil (~22ºS) to central Argentina (~42ºS). Two distinct patterns in habitat use by depth were observed between 22 and 42ºS: in southeastern Brazil, sightings were restricted to coastal waters, with depths ranging from 18 to 70 m. On the other hand, in the area that extends from southern Brazil to Central Argentina (from 28°S to 42°S), sightings were recorded in deeper waters, ranging from 71 m to 1,435 m, in the outer shelf and break. The cranial analyses showed that both short and long-beaked forms occur in the SWA. In conclusion, the genus Delphinus seems to occur associated to areas of higher productivity in the SWA. One stock seems to be associated with the productive waters discharged by the Amazon River and possibly with the coastal upwelling system off the coast of Venezuela, while the other two stocks are associated to the Cabo Frio upwelling system, in the case of southeastern Brazil and the Subtropical Convergence in southern Brazil, Uruguay and Argentina.