O Boto-cinza (Sotalia guianensis) no complexo estuarino lagunar de Cananéia: fatores associados ao uso de habitat

Abstract

Niche modelling can be used to determine the distribution of a particular species in an enviromental space (ecological niche). It may be important to help to preserve endangered species. Therefore, in this study, niche modelling was used to evaluate the influence of: the habitat; the artisanal fishermen‟s catch species; and the Valo Grande on the presence of the Guiana dolphins (Sotalia guianensis) in the Estuarine Lagunar Complex of Cananéia, Brazil. The data were collected in three fieldworks per season, from January 2012 to November 2014. The fieldworks took place in four predefinied sectors. These sectors were sampled using a line-transect method. The presence of the Guiana dolphin was observed mostly on sector II. Probably because of the proximity to the adjacent ocean. The distribution among sectors was more homogeneous in the short cool season, when the environmental variables are more stable. The larger dolphin clusters were found during the winter. Guiana dolphins were sighted in a great diversity of environmental conditions. Nonetheless, the highest occurrences were recorded in cooler and turbid waters; depths greater than 10 meters; salinity above 10 ppm; and during spring tides (technically known in Portuguese as 'maré de sizígia'). Furthermore, the presence of an artisanal fish trap, known locally as cerco-fixo, has positively influenced the occurrence of Guiana dolphins in the estuary. The dolphins use cerco-fixo fish traps to corner shoals and reduce the escape routes of their prey. The mullet (Mugil brasiliensis) was the fish species which had the highest positive correlation with the presence of dolphins, followed by the leatherjacket (Oligoplites saurus) and the tripletail (Lobotes surinamensis). On the other hand, the white mullet (Mugil curema) and the whiteleg shrimp (Litopenaeus vannamei) had a negative correlation with the presence of the Guiana dolphin. The data collected on the Valo Grande Channel showed that freshwater discharges decrease the presence of Guiana dolphins. We can conclude that the Guiana dolphins have an heterogeneous distribution within the studied estuary. Therefore, the areas of greatest ocurrence deserve greater attention in the development of preservation strategies.