Ecologia populacional e comportamento do boto-cinza, Sotalia guianensis (van Bénéden, 1864), na enseada do Mucuripe, Fortaleza, estado do Ceará

Abstract

In the state of Ceará, the guiana dolphin, Sotalia guianensis, inhabits a highly disturbed open area: the Mucuripe bay, in Fortaleza.. In this region, important information for identification of the conservation status of the species, as well as the identification of conservation measures are unknown, such as population parameters, behavioral and space usage. Thus, the study presented here sought to fullfill some of these gaps. The estimated population abundance of dolphins in the study period was only 41 animals (26-64), the lowest estimated to date for the species. The apparent survival rate of adults was 0.88, below estimates for other populations of coastal dolphins. The Mucuripe bay is a feeding and parental care area for the guiana dolphin, which occur in the region throughout the year, mainly in four locations: Marina Park, Iracema beach, Mucuripe harbour and Ideal breakwater. At these locations, the dolphins use the structure of piers and breakwaters to facilitate the capture prey cooperatively. Greater abundance of dolphins was recorded during low tide, when it is probably easier to catch the fish cooperatively. The guiana dolphin groups recorded were small, with an average of 4.1 and a maximum of 8 individuals, which may be related to food availability. Groups with calves and during the socialization behaviors were higher. Dolphins frequency of use of the Mucuripe harbour decreased in the months when dredging operations were recorded. Sixty percent of the 25 photo-identified animals were considered residents, with degree ranging from 9 to 40%. The animals showed a preference for areas less than 400m away from breakwaters/piers, between 400 and 800m from the coast and at depths between 3 and 6 meters, in that order. The proximity of breakwater and piers was the characteristic that most influenced the habitat use of the species in the bay. In these places there is a concentration of prey and animals have specialized in using the structures to corral fish. The area of use of the species in the sampled area was 11.56 km2. The preferred use area decreased during the second year of study, when there was an increase in activities of dredging in the Mucuripe harbor channel and the animals practically abandoned this region. The percentage of overlap between the area of use of the dolphins and fishing activity in the study area was 25%. The overlap area of use of the dolphins to the area of use of motorboats was 70% throughout the study period. The results indicate that urgent action must be taken to reduce the impact of human actions on the guiana dolphin, as the identification of areas for restricting more impactful activities. Since the dolphin population is very small and the minimum recorded mortality is unsustainable, if such measures are not taken immediately, the local extinction of the species will be inevitable.