Movement patterns of franciscana dolphins (Pontoporia blainvillei) in Bahia Anegada, Buenos Aires, Argentina

Abstract

From January 1993 to July 1999, systematic sightings of franciscana dolphins were conducted from four shore- based stations in Bahia Anegada, Argentina. Data were recorded using focal animal/group sampling methods. This study tested the hypothesis that dolphin movements within Bahia Anegada were random, assuming independence of sightings. The trend in dolphin swimming movement was defined as a direction scored as “coming in”, “neutral”, and ”going out”. In total 338 sightings were recorded, with a total effort of 2674 hours. The relative frequency of franciscana sightings demonstrated that movement was significantly dependent on tidal state, rejecting the hypothesis that dolphin swimming directions within the study area are random. Significant associations were also observed in the relative frequency of sightings in relation to the shore-based stations, suggesting a differential use of the bay’s habitats perhaps due to location of prey, tidal current speed, depth, and topography of the coast.