Abstract
Indo-Pacific humpback dolphins (Sousa chinensis) typically inhabit turbid coastal waters and estuaries, making it hard to observe their behaviour. Therefore, until now, only a few studies have provided descriptions of this species’ behaviour. Studying foraging behaviours is needed to better understand the tactics adopted by the species and inform conservation measures. This study aimed to describe and quantify the foraging behaviours displayed by Indo-Pacific humpback dolphins in three different locations in the northern South China Sea, including Beibu, Zhanjiang, and Pearl River Delta (PRD). Dolphins were observed side breaching, half-side breaching, fish shoal pursuing, mud foraging, foraging around gillnets, seine nets, trawlers, shellfish farms, fish farms, and wind farms. No cooperative foraging was observed and animals were mostly engaged in individual and group random feeding. Differences in foraging behaviours were found among the three studied geographic populations with Zhanjiang dolphins foraging in large and dispersed groups and using fish farm surroundings as a foraging ground; PRD dolphins foraging in small groups with various dispersion modes and engaging in mud foraging and foraging in association with pair trawlers or seine fishing; and Beibu dolphins foraging in small groups with various dispersion modes like those from PRD but unlike them, seldom displaying side or half-side breaches. The observed variations in group size and cohesion, movement patterns and behaviour, or associations with human activities reveal the complexity of this species’ foraging behaviour and differences among populations that may be linked with the characteristics of the environment dolphins live in.