Spatial distribution of river dolphins, Inia geoffrensis (Iniidae), in the Araguaia River (central Brazil)

Abstract

This study aimed to characterize the distribution of botos, Inia geoffrensis, along a 530 km stretch in the middle reaches of the Araguaia River (central Brazil). Data collection was conducted in May (lowering water season) and September (dry season) of 2009. The location and group size of botos were recorded, and the relative density was calculated. The river was divided into nine areas according to geomorphological features; these areas were later grouped into two (low and high) levels of sediment input. The study area was categorized into six types of shoreline habitats: vegetated bank, non-vegetated bank, beach, confluence, bay, and island. A total of 195 sightings (239 botos) were recorded, with the highest density of sightings found in habitats in which tributaries entered the Araguaia River (confluence) followed by the bay habitat. The group size varied from one to three individuals, and single individuals were predominant. The segment with high sediment input also had a higher density of botos compared with the low-sediment segment. Botos-preferred habitats and human activities have a great overlap in Araguaia River. Restrictions of certain human activities, and tourism management would reduce both the intentional and accidental harm of botos in the Araguaia River.