Hábitos alimentares do boto cinza (Sotalia guianensis, Van Bénéden, 1864) (Cetacea: Delphinidae) nas baías de Sepetiba e da Ilha Grande (RJ)

Abstract

Cetaceans influence the entire dynamics of an ecosystem, as they are the main consumers at different trophic levels and understanding this function provides data capable of assessing the due impact of their predation on different prey populations and on the structure of these communities. The Guiana dolphin (Sotalia guianensis) is a Delphinidae specie that occurs in coastal and estuarine waters, from Honduras to Santa Catarina (BR), and its main food is fish, cephalopods, and shrimp. The objective of this study was to investigate the feeding habits of the Guiana dolphin in Sepetiba bay and Ilha Grande bay, analyzing the main prey consumed and comparing them in relation to sex, sexual maturity, seasonality and between bays during 2007 to 2021, including the unusual mortality caused by cetacean morbillivirus. The analyzes were carried out from the stomachs collected from 419 Guiana dolphins in Sepetiba Bay and 95 Guiana dolphins in Ilha Grande Bay. Prey were identified with the aid of reference collections and length and biomass estimates were performed using regression equations found in the literature. In total, 42 species of prey were identified in Sepetiba Bay and 30 species in Ilha Grande Bay, with teleost fish of the Sciaenidae family being the most found. The Guiana dolphin, in both bays, presented a predominantly teleost fish diet, followed by cephalopods and shrimp. The most representative teleost fish in the Sepetiba bay was the whitemouth croaker (Micropogonias furnieri) and in the Ilha Grande bay it was the toadfish (Porichthys porosissimus). Among the cephalopods, the most representative species was the squid Doryteuthis plei in both bays. It was not possible to analyze the importance of shrimps. The Guiana dolphins were divided into four groups for analysis according to sex and sexual maturity: immature females, mature females, immature males and mature males. In Sepetiba Bay, the most representative teleost fish for mature male Guiana dolphins was the Atlantic achoveta (Cetengraulis edentulus) and for the other Guiana dolphins it was the whitemouth croaker. In the Ilha Grande bay, the toadfish was the most important for the mature Guiana dolphins (females and males), however for the immatures the most representative teleost fish differed between the gender. The squid D. plei continued to be the most representative cephalopod for all groups. Regarding seasonality, the greatest abundance and richness of prey was in the auntumn/winter season, but there were no changes in the most representative prey. During the morbilliviruses event, more than 70% of stomachs were found empty. Therefore, this study is an important contribution to the knowledge of the feeding habits of the Guiana dolphin populations in both bays. Since there are few detailed records on feeding habits in the literature, they reinforce the importance of conservation and management of the species, as well as the importance of preserving the regions.