Distribution and habitat characteristics of dolphins of the genus Stenella (Cetacea : Delphinidae) in the southwest Atlantic Ocean

The distribution of dolphins of the genus Stenella is poorly known in the southwest Atlantic Ocean. A complete review of records (n = 311) of these dolphin species was performed to describe distribution and habitat. Atlantic spotted dolphins S. frontalis occur in both southern (21 to 33 degrees S) and northern Brazil (north of 06 degrees S), with a hiatus in its distribution off eastern South America. This species presents the highest preference for nearshore habitats, restricted to waters within the 1000 m isobath. Pantropical spotted dolphins S. attenuata are found in tropical waters as far south as 22 degrees S and are mainly observed off northeastern South America. They occur beyond the continental shelf break in depths >850 m. Clymene dolphins S. clymene are distributed in deep waters (1390 to 4500 m) as far south as 30 degrees S. Strandings are more common where the continental shelf is narrower. Spinner dolphins S. longirostris are found in oceanic waters as far south as 30 degrees S. They inhabit tropical waters over the shelf and slope (depths ranging from 170 to 2700 m). The striped dolphin S. coeruleoalba is the least known species of the genus in the western South Atlantic. Most records are from temperate waters in southern Brazil and Argentina. The distributions of S. attenuata, S. clymene and S. longirostris overlap to a great extent and are predominantly oceanic and associated with warm ocean currents. S, frontalis seems to prefer a different, coastal habitat, influenced both by warm currents and upwelling areas. The discontinuous distribution of this species suggests that an isolated population inhabits the southern coast of Brazil.