Natural history of dolphins of the genus <i>Sotalia</i>
AbstractGeneral biology, including food habits, reproduction, age and health of the dolphins of the genus Sotalia, are reviewed according to current scientific knowledge. At least 25 teleost fish families, 5 cephalopod families and 1 crustacean family are included in the diet of the Guiana dolphin (S. guianensis), while up to 13 fish families were identified in the stomachs of the tucuxi (S. fluviatilis). Among the fish consumed by Sotalia spp., the schooling fish are the most common ones and both dolphin species use similar foraging strategies. However, due to the completely different ecosystems used by them, prey species consumed by these dolphins are also different. The maximum age of incidentally caught Guiana dolphin was 30yr and the maximum age estimated in the tucuxi was 43yr. The maximum total body length and weight reached by S. guianensis was 222cm and 121kg, respectively, and for S. fluviatilis 152cm and 53kg, respectively. Sexual maturity in the Guiana dolphin was estimated to occur at 170-180 cm in males, and 160-169 cm in females, while onset maturity in the tucuxi occurs at around 140cm in males and 132-137 cm in females. Ovulation apparently occurs only in the left ovary of the tucuxi, while both ovaries of the Guiana dolphins are functional. The proportion of testes mass in relation to total body mass in adult males can reach up to 5% in the tucuxi, and 3.3% in the Guiana dolphin, suggesting a promiscuous mating system with sperm competition in both species. Although seasonal birth peaks can occur in Guiana dolphins, they seem to reproduce throughout the year. However, the tucuxi presents defined birth seasonality, with most females giving birth during the low-water season in the Amazon. We suggest maintaining S. fluviatilis in the ‘Data Deficient’ category of the IUCN Red Data Book. Nevertheless, due to the recent recognition of S. guianensis as a species, its conservation status has not been assessed yet. This species, however, deserves special attention as it is strongly subjected to anthropogenic pressures throughout its distribution.
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