Golfinhos-de-dentes-rugosos, Steno bredanensis (G. Cuvier in Lesson, 1878), em águas costeiras do estado do Rio de Janeiro, Brasil

Abstract

Investigate ecological aspects of behavioral activities, group characteristics and habitat use in parallel with population parameters, site fidelity and population size is of utmost importance to understand species/habitat relationship. Including coastal areas from Brazil, Steno bredanensis is a poorly known species which was investigated in the present study through Guanabara Bay and adjacent areas. This study was divided into two Sections, where Section 1 is aimed at investigating Steno bredanensis behavioral activities, group characteristics, habitat use and the relation with physical environmental variables, while Section 2 is aimed at investigating site fidelity, movement, population parameters and population size through mark-recapture techniques. Between 2009 and 2017, S. bredanensis was observed in different behavioral activities, although feeding was the most frequent among them (55,6%). Seasonal variation was reported for feeding (X² = 38.289; df = 3; p = 0.0001) and traveling (X² = 39.000; df = 3; p = 0.0001) behaviors. Group size varied between two to 50 individuals N = 80; 21.3 ± 12.3) that varied annually (Kruskal-Wallis, N = 80, p = 0.001) but not seasonally (Kruskal-Wallis, N = 80, p = 0.682). Behavioral activities did not show any evidence to be influenced by group sizes (Kruskall-Wallis, N = 74; p = 0.93). Calves presence had influence in group sizes (Mann-Whitney U = 122.5; p = 0.0001) and were more common in bigger groups. Group geometry was not influenced by their sizes (Kruskall-Wallis, N = 76; p = 0.12) and mixed groups were more frequent (72.8%). Steno bredanensis showed preferences to depths between 10-20 m, selecting areas through the study site. Kernel Density showed that groups utilized a total area of 107 km² (K95%) and core areas of 16.5 km² (K50%) located alongside the entrance and internal areas of Guanabara Bay. Behavioral activities were related to declivity (Kruskall-Wallis, N = 71; p = 0.04). CTD samples showed mean sea surface and bottom temperatures of 21.9 °C and 17.8 °C, respectively and group sizes were positively correlated to sea surface temperatures. Photo-identification allowed the identification of 173 marked individuals that had different frequencies of occurrence in the study area varying from 0.9 to 72.7%. Recaptures between consecutive days varied from zero to 18 individuals (5.0 ± 4.0). Under Pollock s Robust Design Steno bredanensis showed high survival index (S = 0.99; SE = 0.0001) that did not vary in time and capture probabilities that vary through occasion from 0.07 (95% IC 0.06 0.08) to 0,92 (95% IC 0.88 0.95). Migration probability estimates showed that movements of S. brenanensis varied through time, where γ varied from 0.21 (95% IC 0.06 0.52) to 0.90 (95% IC 0.52 0.99), whileγ varied from 0.26 (95% IC 0.13 0.45) to 0.95 (95% IC 0.63 0.99). The number of individuals that utilized the study area varied seasonally from 13 (95% IC 10 18) to 80 (95% IC 76 84) individuals for 2012/2013 (November-February spring/summer) and 2010 (May-July autumn/winter), respectively. POPAN model showed constant survival (Φ = 0.99, SE = 0.0001) and probability of entrance (pent = 0.03; SE = 0.01), although capture probabilities varied in time. Correcting population size and adding the proportion of unmarked individuals, the population of Steno bredanensis that utilized the study area from 2010 to 2017 was estimated in 218 individuals (95% IC 202 241).