Estimativa de parâmetros populacionais do boto-cinza, Sotalia guianensis (Van Bénéden, 1864) (Cetacea, Delphinidae) na Baía de Paraty (RJ)

Abstract

Number of studies involving estimates of cetacean population parameters based on photo-identification data has grown over the years. In Brazil, there are few studies of cetaceans using this approach, however, they are increasing, especially with the species Sotalia guianensis (van Bénéden, 1864), known as Guiana dolphin. The aim of this study was to estimate the survival probability, capture probability, migration and abundance of the population of the Guiana dolphin in Paraty Bay (RJ, 23º07'S 44º33'W) using models of mark-recapture based on photo-identification data, between 2005 and 2009. Surveys were conducted between August 2005 and July 2009 in an out-board powered boat. Pictures of dorsal fins were taken using a Canon 20D digital camera equipped with zoom lenses 100-400mm. Sixty field trips were conducted in Paraty Bay totalizing 172 hours of field effort and 72 hours of photographic efforts. A total of 27,892 photographs were taken on 42 sightings of Guiana dolphins and 6612 photographs (23.7%) were considered appropriate for photo-identification purposes. A total of 621 individuals were cataloged based on permanent marks on the dorsal fin. The individual encounter histories were analyzed using program MARK. The survival ranged from 0.82 (± 0.05) to 0.85 (± 0.05) and the capture probability ranged from 0.16 (± 0.04) to 0.40 (± 0.06). The number of marked individuals in the population estimated by the Jolly-Seber model was N = 586 (± 114.66) (CI: 361-811). The proportion of marked animals in the population was 0.66 (± 0.03) and the total abundance was 884 individuals (± 176.8) (CI: 602-1296). The probability of temporary emigration (γ``) and stay out of the area (γ') was 0.43 (± 0.07) and the capture/recapture probability ranged from 0.01 (± 0.01) to 0.42 (± 0.05). The probability of staying in the area (1 - γ``), as well as the return probability from temporary emigration (1 - γ') was 0.57. Despite the significant movements of transient individuals, since the sampled area is smaller than the home range estimated for the specie, the results indicate a moderate residence of the Guiana dolphin. The total annual abundance ranged from 325 in 2005 to 448 in 2009. The power analysis determined that it would be necessary nine years of study to observe a tendency of decline of 5% in population size. Paraty Bay harbors one of the largest populations of Sotalia guianensis.