RIVERINE HABITAT PREFERENCES OF BOTOS (INIA GEOFFRENSIS) AND TUCUXIS (SOTALIA FLUVIATILIS) IN THE CENTRAL AMAZON

Abstract

The distribution and density of the Amazon's two contrasting endemic dolphins–boto, or Amazon river dolphin, Inia geoffrensis, and tucuxi, Sotalia fluviatilis–were examined on two adjoining large rivers in western Brazil. Using a 17‐m river boat as a sightings platform, strip transects were used to cover areas within 150 m of the river margin and line transects were used in all other areas. Highest densities of both dolphins occurred near the margin, and lowest in the center of rivers. Seven different habitats were identified along river margins. The boto and the tucuxi differed in some elements of habitat choice, but they shared a preference for areas with diminished current and where two channels joined. Neither species favored the two most common edge types in this region of the Amazon‐mud banks and flooded forest margins. Overall, the most preferred habitat type was the least common, and known as “meeting of the waters.” In these areas a channel of sediment‐rich white water meets one carrying acidic black water; the resultant mixing produces particularly productive, and obviously attractive, conditions for dolphins. These results demonstrate that Amazonian dolphins selectively occur in areas known to be favored for gill net deployment by local fishermen, and may explain why entanglement is apparently a common cause of mortality.

Mudanças no Código Florestal e seu impacto na ecologia e diversidade dos mamíferos no Brasil

“…(Ayres 1993), outras usam as várzeas em seus ciclos anuais e habitats complementares, como o peixe-boi da Amazônia, cujo ciclo de vida está diretamente associado às várzeas, onde se reproduzem e se alimentam durante os períodos de enchente e cheia, quando ocorre maior abundância de macrófitas aquáticas (da . Indiretamente essas alterações podem afetar as duas únicas espécies de cetáceos de água doce do Novo Mundo (Inia geoffrensis e Sotalia fluviatilis) que ocorrem em maior densidade nas áreas de várzea, em função da grande diversidade e abundância de peixes quando comparadas a outras áreas da sua distribuição (Martin et al 2004, Faustino & da Silva 2006.…”

Accelerating population decline of Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis)

“…), the Amazon River dolphin (Inia geoffrensis), the Irrawaddy dolphin (Orcaella brevirostris) and the tucuxi (Sotalia fluviatilis), also face comparable challenges of long-term survival (Reeves et al, 1991;Reeves and Chaudhry, 1998;Smith and Smith, 1998;Smith et al, 2001;Martin et al, 2004;Braulik, 2006), but demographic data for these species are still extremely limited. Although specific threats facing these freshwater cetaceans may vary geographically in their importance, common threats include substantial loss of effective habitat (Reeves et al, 1991;Braulik, 2006), increasing concentrations of persistent organic pollutants in cetacean tissue (Senthilkumar et al, 1999), and incidental fisheries by-catch (Martin et al, 2004). The drastic decline of the Yangtze finless porpoise in two decades as a result of rapid industrial and economic growth reveals how uncontrolled environmental deterioration threatens the future of freshwater cetaceans despite the potential for the massive scale of the Yangtze system to buffer anthropogenic impacts.…”

Dolphins as Indicators of Micropollutant Trophic Flow in Amazon Basin

“…The former city (Porto Velho) presents a population of about 370 000 people, while in the latter, the number is > 60 000 (IBGE 2008). Although three out of the four dolphins analyzed by Torres et al (2007) have been found in a preserved environment (Mamirauá Reserve), data obtained from individually marked dolphins demonstrated that Tefé area is within the movement range of the boto population that inhabits the quoted reserve (Martin et al 2004), which could explain the occurrence of high concentrations of a pollutant of industrial and/ or urban origin (PCB) in an Amazonian reserve. Even though further investigations comprising a larger sampling are required before strong conclusions can be reached, it is important to highlight that ΣPCB concentrations in the subcutaneous adipose tissue of cetaceans from Amazon seem to mirror human presence in the concerned area.…”