A first estimate of franciscana (Pontoporia blainvillei) abundance off southern Brazil

Abstract

The franciscana, Pontoporia blainvillei, is endemic to the western South Atlantic Ocean and is perhaps one of the most threatened small cetacean species in this region. This paper presents a first abundance estimate for the coastal waters of Rio Grande do Sul State (southern Brazil) and Uruguay. In March 1996, an aerial survey was conducted along the Rio Grande do Sul State coast. Thirty-four franciscanas (29 groups) were recorded leading to a mean density estimate of 0.657 individuals/km2 (95% CI: 0.516 to 0.836) for the study area (435km2) after applying a correction factor for submerged dolphins. This corresponds to an estimated abundance of 286 franciscanas (95% CI: 225 to 364). The study area represents only 0.7% of the suggested distribution of the stock. The paper discusses possible management implications of this study in the light of reported incidental mortality estimates for this region. Further surveys covering a larger area are recommended in order to obtain more reliable abundance estimates for the stock.