Características do comportamento alimentar coordenado do boto-cinza Sotalia guianensis (Van Béneden, 1864) (Cetacea: Delphinidae) nas Baía de Sepetiba e Baía de Ilha Grande - RJ

Abstract

The present study characterized the coordinated feeding behavior of two populations of estuarine dolphin Sotalia guianensis in southeastern of Brazil. In both bays were investigated coordinated feeding bouts, frequency of mean coordinated feeding tactics (Wall formation, Line Abreast, “Kettle” and Perpendicular feeding), presence of jumps, group size engaged in each tactic, seasonality and presence of calves and juveniles during the coordinated feeding behavior. In Chapter 1 the coordinated feeding behavior of the Sepetiba Bay population was analyzed based on 29 boat trips of which 18 occurred in spring-summer period and 11 occurred in autumn-winter period from September 2000 to August 2001. In Chapter 2 a data comparison between Sepetiba Bay (Chapter 1) and Ilha Grande Bay populations (collected from May 2007 to March 2008) was made. Were observed 370 mean feeding tactics in Sepetiba Bay and 914 in Ilha Grande Bay. In a total, were quantified 239 feeding bouts with mean duration of 66,65s in Sepetiba Bay and 399 “bouts” in Ilha Grande Bay with duration of 60 s ± 114 s. Statisticals differences of feeding bouts were encountered between the autumns-winter periods for the two bays with Sepetiba Bay presenting longer feeding bouts and higher frequency of tactics in the autumn-winter period than spring-summer period, and the opposite result for Ilha Grande Bay. In both bays, Wall formation was the feeding tactic more used by dolphins and with bigger group size, suggesting that this tactic has a better cost benefit relation for these two populations. The presence of jumps was observed, being more frequently seen in Ilha Grande Bay. In Sepetiba Bay, group size was significantly different between all feeding tactics, but showed no statistically difference for each tactic separately along the seasons. Among the two bays Mood´s Median test only showed significant difference in group size for the feeding tactics Wall formation and Line Abreast. Kruskal Wallis test was significantly different in group size for all feeding tactics along the seasons in the two bays. These differences in group size seems to be related with the chosen prey and the energy intakes of each tactic for each participant of the group. In Sepetiba Bay, calves and juveniles were observed in 227 groups (61.35%) whereas in llha Grande Bay these animals were present in 905 feeding tactics, being the frequency of feeding tactics with presence/ausence of these animals between the two bays statistically different. So, this estuarine complex is an ideal region for breeding and social learning of the several feeding tactics by the calves and juveniles. These regions can be considerate as important areas for this species conservation, requiring more management and preservation efforts.