Activity budgets and distribution of bottlenose dolphins (<i>Tursiops truncatus</i>) in the Patos Lagoon estuary, southern Brazil

Abstract

The common bottlenose dolphin, Tursiops truncatus, is one of the world's best known cetaceans. However, there are few studies on the activity budgets and distribution of this species along the Brazilian coast. This study aimed at describing and quantifying the behavioral activity of T. truncatus in the Patos Lagoon Estuary, Rio Grande do Sul state, southern Brazil (ca. 32°09'S, 52°05'W). The study area was divided into three sub-areas according to the proximity to the estuary mouth. The behavioral data were gathered every 5 minutes following a focal group sampling approach. A total of 34 boat surveys were conducted between December 2001 and January 2003, totaling 66.95h of direct observation and 672 records of behavioral activities. The first 15 minutes of each group encounter were discarded to avoid the influence of the boat approach on dolphin behavior. The most observed behavior was feeding (37.64%), followed by traveling (29.17%), travel-feeding (21.87%), socializing (5.8%), milling (4.33%) and resting (1.19%). There was not a significant difference among the frequencies of commonly observed behaviors: feeding, traveling and travel feeding (p<0.05, t-test for proportions). Dependence between activity and season was detected in subareas I and II (p<0.001; Pearson's Χ²), as well as an association between activity and sub-areas (p<0.001; Pearson's Χ²). Regarding group size, 56.41% of the activities recorded were carried out by groups of 1 to 3 dolphins, 31.63% from 4 to 6, 10.25% from 7 to 10, and 1.71% by groups with more than 10 individuals. This study confirmed the importance of the Patos Lagoon Estuary as an area for bottlenose dolphins to conduct their daytime activities, in particular feeding.