Abstract
The franciscana dolphin, Pontoporia blainvillei, is endemic to the western South Atlantic Ocean and has been considered the most threatened small cetacean in this region. For this reason, abundance estimates were recognised and recommended as a research priority long time ago, first at the Workshop for the River Dolphins carried out at Wuhan in 1986 (Perrin et al., 1989) and also at the following workshops carried out in Argentina and Brazil (Crespo, 1992; Pinedo, 1997). Population size estimates were needed to provide baseline information and allow a comparison with mortality rate estimates for different areas of the franciscanas range, especially as some of those mortality rate estimates were suspected to be unsustainable. The delay in achieving such objective was in part a result of a lack of human resources in the region with the appropriate methodological training in both field work and data analysis for abundance estimation, as well as due to financial constraints. The opportunity for a first survey was given in March 1996.
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