Abstract

Mariana Freitas Nery, Sheila Marino Simão and Tereza Pereira

The dynamics of habitat utilization by Sotalia guianensis has been investigated. Between January 1997 and May 1998, 145 h of direct observations were made from a fixed location at Ponta do Zumbi on Marambaia Island, and 249 groups of dolphins were sighted. Initial and final times of the observation, approximate location, presence of calves, activities performed by the dolphins and prevailing weather conditions were recorded for all sightings. Dolphin groups were observed during all seasons of the year, and sightings occurred mainly during the late morning (9:00 - 11:59 h) and early afternoon (12:00 - 14:59 h). Dolphins exhibited a preference for the sheltered sub-areas of the bay rather than for the subarea adjacent to the open sea. The most commonly observed aggregation of animals consisted of groups of 1 – 10 individuals. The activities performed by the dolphins were, in decreasing order of frequency of occurrence: foraging/feeding, travelling, socialization and resting. Daily and seasonal profiles of dolphins activities were dictated by many interacting factors (temporal, environmental and population characteristics), none of which could alone explain the manner in which the animals utilize the area or the organization of life cycle in the habitat.