Padrões de associação e uso do habitat de machos adultos de boto-vermelho (Inia geoffrensis) (Cetacea: Iniidae) na Reserva de Desenvolvimento Sustentável Mamirauá

Abstract

The association patterns and habitat use of adult males of Amazon river dolphin (Inia geoffrensis) were investigated on Sustainable Development Reserve Mamiraua, Central Amazon, Brazil. For the study were analyzed the sightings of 14 adult males of Amazon river dolphin, all with more than 200cm in body length, more than 10 years of age and identified in the field by cryogenic marks previously applied. All individual have more than 10 sightings (min. 11 – max. 83) and a total of 638 sightings were analyzed. To quantify the associations was used the simple ratio index (SR) and sighted individuals in same group were considered as ‘in association’. All analyzes were performed in the SOCROG program version 2.4. In all analyzes, completed hydrological cycle (2008-2009), hydrological phases (rising, flood, lowing and dray) and habitats (lake, paraná, confluence, river and beach), the level of association between individuals was extremely weak, with high proportion of dyads with index equal to zero and without presence of preferred companions and/or avoided of short and long-term. The result corroborates to the solitary behavior described for the species and indicates that adult males of Amazon river dolphin don’t form alliances of males. The adult males of Amazon river dolphin tend to associate more strongly in the river and beach habitats, however, these associations are random. The lack of naturals predators, abundance of food and the behavior agonistic typical of adult males for access to female in estrus appear to exert strong influences on level associations of adult males of Amazon river dolphin. Regarding the use of the habitat, the frequencies of the sightings were significantly associated with habitats aquatics and varied seasonally. In all the hydrological phases the confluence was the habitat aquatic more used by adult males of Amazon river dolphin in the area of study. Seasonal differences in values of SPUE (Sightings Per Unit of Effort - in hour) in aquatic habitats were not statistically significant, but were related to the lateral migration of fish. The adult males of Amazon river dolphin tend to use more often the most productive habitats, that allow the migration of the fish and the have large prey densities.