Uso de habitat peloboto-cinza (Sotalia guianensis, van Benédén, 1864) nas baías doestado do Rio de Janeiro

Abstract

The Guianadolphin Sotalia guianensis(Cetacea: Delphinidae) is a species that, due to its coastal habit, deals with exposure to innumerous anthropogenicthreats. The Guiana dolphinconservation status is classified as "Neart Threatened" by IUCN and "Vulnerable" by ICMBio, which makes it essential to understand its ecology in order to preserve thespecies. Thus, the aimof the study was to investigate the habitat use of Guiana dolphins(Sotalia guianensis) in three bays of Rio de Janeiro state between 2017 and 2019: Guanabara Bay (BG), Sepetiba Bay (SEP) and Ilha Grande Bay (BIG). From May 2017 to May 2019, surveyson board ofmotor boats werecarried out in the three bays,resultingin 33 surveysand 39 groups observed inBG, 90 surveysand 277 groups inSEP and 96 surveysand 115 groups in BIG. The information collected included animal behavior, groupsize and composition (presence and number of calves) and local depth. Field data were computed and processed. Non-parametric tests were used in the statistical analyzes (Kolmogorov-Smirnov normality test, p <0.01).Significant differences were observed when analyzing behavior frequencies in the three bays (X2= 52.3602; gl = 2; p < 0.00001), although feeding was the dominant activity (Proportions: 84.2% in BG, 73.3 % in SEP and 53.1% in BIG). Group characteristics (Kruskal-Wallis group sizes: H2.715= 70.641; p < 0.0001; Kruskal-Wallis number of calves per group: H2.715= 87.305; p < 0.001) and depth selection (Kruskal-Wallis, H2.715= 217.947; p < 0.001) also varied between the three bays. Small groups (Mean +SD = 18.6 +5.4) containing up to 3 calves (Mean +SD = 2.0 +0.8) were observed in shallower depths in BG, from 3.2 to 15 m (Mean +SD = 5.4 +2.2). In SEP and BIG, large groups of 1 to 225 (Mean +SD = 37.1 +49.5) and 1 to 500 individuals (Mean +SD = 74.7 +77.0) were registered, respectively, containing many calves (SEP: Mean +SD = 3.3 +6.9; BIG: Mean +SD = 8.9 +14.5). BIGpopulation selected intermediate depths (Mean +SD = 11.2 +4.7; Min -Max = 3 to 26.3 m) and the Guiana dolphins from SEP occupied relatively deeper waters (Mean +SD = 13.5 +5.8; Min -Max = 3 to 36.5 m). Diurnal variations in habitat use were observedin BG and BIG and seasonal differences were only observed regarding thegroup size in SEP (Kruskal-Wallis, H3.386= 21.029; p = 0.0001). Daytime and seasonal variations were attributed as a consequence of local prey dynamics in each study area. The main conclusion is that Guiana dolphins use the studied bays differently, according to biotic and abiotic factors and also according to the intensity of anthropic activities.