Abundance estimation of franciscana dolphins by means of aerial surveys in Buenos Aires Province, Argentina, with comments on mortality rates

Abstract

Between October 11 and 16, 2019, and March 12 and 14, 2022, 9 flights were made on the coast of the province of Buenos Aires in meteorological conditions that allowed the sighting of several species of cetaceans. The two series of surveys (2019-2022) had to be carried out separately because of travel restrictions associated with the covid-19 pandemic. This document reports on results, including estimates of abundance, for franciscana dolphins (Pontoporia blainvillei). The number of sightings (and indviduals) in 2019 and 2022 were 41 (68 individuals) and 55 (80). Abundance for FMA IVb was estimated to be 8351,01, while FMA IVc was 2336,28. The total abundance of Franciscana for both areas would preliminary give a figure of 10687 dolphins if we consider the estimation obtained in 2022 plus 5896 dolphins estimated in 2004 for the southern areas, roughly 16600 individuals without considering those in deeper waters beyond the 30 meter isobath. In addition to franciscanas, several groups of common and dusky dolphins were observed during the aerial surveys, some very numerous.