Uso do habitat, fidelidade de sítio e parâmetros populacionais do golfinho-pintado-do-Atlântico, Stenella frontalis (G. Cuvier, 1829), na Baía da Ilha Grande (RJ).

Abstract

Ilha Grande Bay currently has at least six common small cetacean species, including Stenella frontalis. Despite Atlantic spotted dolphins having coastal habit, information has been based on brief encounters. Therefore, the goal of the present study was to describe group characteristics and surface behavioral, habitat use, site fidelity, and abundance of this species in a coastal environment in southeastern Brazil. A total of 132 days of boat surveys were made between June 2017 and January 2020, where twenty-six groups were observed. Stenella frontalis used depths between 16.5 and 35.2 m, selecting specific areas in the study site. Kernel Density showed that groups utilized a total area of 242.7 km² (K95%), with a core areas of 46.5 km² (K50%) located in the western region of the bay. The groups were observed performing different behavioral activities, although traveling (59.6%) was the most common behavior, mainly in autumn and winter. However, behavior showed no significant variation in relation to seasonally (X² = 9.85; df = 6; p = 0.131). Traveling and foraging/feeding behaviors varied significantly (Kruskal-Wallis, H2, 45 = 12.4; p = 0.0020) regarding the depths at which they were observed. Group size varied between nine to about 200 individuals (94.3±57.6), with groups larger than 100 dolphins observed in 36% of the total encounters. Group size varied regarding depth (Spearman, N = 53, R = 0.506; p = 0.000112), but not seasonally (Kruskal-Wallis, H3, 53 = 2.18; p = 0.535). Photo-identification technique allowed the identification and cataloging of 234 individuals marked, and new identifications were made until the last survey. Resighting indices varied from 0.13 to 0.75 (0.26 ± 0.16), with only three individuals at the maximum value. The seasonal occurrence ranged from 0.25 (individuals sighted in one season only, n = 106) to 1 (individuals sighted in all seasons, n = 22). POPAN model showed Stenella frontalis has a high survival (Φ = 0.94 - 1.00) which varied over time. Capture probability (p = 0.00 - 1.00) in the population also varied over time, although entry probability (pent = 0.03; SE = <0.01) remained constant. Correcting population size to include the unmarked individuals, the population of Stenella frontalis that utilized the Ilha Grande Bay from 2017 to 2020 was estimated in 397 individuals (95% CI = 389-406). The presence of hundreds of dolphins in Ilha Grande Bay reflect in the occurrence this large population along the southeastern waters of Brazil. But due to coastal habit and site fidelity, S. frontalis is facing several ways environmental degradation and anthropic threats. This highlights the importance of Ilha Grande Bay for cetacean conservation proposals that occur along southeastern waters of Brazil alongside the small populations of resident cetaceans.