Group structure of Sotalia guianensis in the bays on the coast of Paraná State, south of Brazil

Abstract

To determine the group structure of Sotalia guianensis on the coast of Paraná State, two bays, Baía de Paranaguá and Baía de Guaratuba, were surveyed between March 1999 and February 2000 and between July 2002 and June 2003 respectively. The heterogeneity of the studied areas was considered a relevant factor, therefore these areas were sectored and each sector was investigated independently. The surveys were carried out through boat line transects and all the animals were registered, even those localized between two transects. The records were taken for the quantity of groups as well as for the amount of individuals in each group and, whenever possible, the individuals were classified as calves or adults. The data were treated both separately and comparatively between the two bays and amongst the sectors of each bay. In Baía de Paranaguá, 735 individuals were registered, divided into 253 groups which varied from 2 to 37 individuals for an average of 2.9 individuals per group. Most of the groups presented a family formation (59.29%) and were observed during the morning. The individuals that were clearly identified as calves represented 24% of the total (176 individuals), adults 55% (405 individuals) and 21% (154 individuals) were impossible to determine. In Baía de Guaratuba, only 32 S. guianensis individuals were observed and distributed into 14 groups for an average of 2.13 individuals per group. These groups varied from 2 to 6 individuals mostly in family formations (50%). The same quantity of individuals and groups was observed during different periods of the day. Of the 32 sampled individuals, 25 (78%) were adults, only one was a calf (3%) and 6 (19%) were undetermined.