Studies show that the infection of cetaceans by socially transmitted diseases may impact the ecology and behavior of individuals and populations. Little is known about the effects of intense, short-term outbreaks of disease, typical of cetacean morbillivirus (CeMV). Understanding these effects is important in the case of resident populations exposed to multiple anthropogenic impacts, as in the case of the Guiana dolphins, Sotalia guianensis, of Sepetiba Bay (BSEP), Rio de Janeiro, Brazil. Two hundred and ten Guiana dolphins died of CeMV in BSEP between November 2017 and March 2018. We investigated whether the outbreak affected the occurrence of Guiana dolphins in the BSEP and whether the size, composition, and cohesion of the dolphin groups shifted significantly. We conducted 25 surveys in BSEP from 2017 to 2019 and found no significant variation between the two periods (pre-CeMV and post-CeMV) in either the occurrence of dolphins or the size, composition, or cohesion of groups. During the pre-CeMV period, 32 groups were observed, with a mean group size of 16.60±21.12 individuals, all groups containing at least one calf, while the “tight” group cohesion pattern was observed most frequently. Eighteen groups were sighted during the post-CeMV period, with a mean size of 23.67±27.51 individuals, with 87.50% of groups containing at least one calf and “mixed” cohesion being the most frequent. We indicate that, over the short term, there was no significant change in the social dynamics of the Guiana dolphin groups in the BSEP after the morbillivirus outbreak, although further monitoring over a longer time scale, and focusing on specific aspects of the species would be necessary to provide more ample insights into the impacts of morbillivirus on this dolphin population. This is important in the context of the cumulative impacts of human activities on this population that have occurred over the past decade.

Climate change alters marine environments, affecting temperature, oxygen levels, and acidity, prompting species to relocate to suitable areas. Understanding these shifts is vital for top predators like cetaceans, crucial for marine ecosystem regulation. We mapped the suitable environments for the rough-toothed dolphin (Steno bredanensis) - considering its limited study in Brazil - and three of its prey: the largehead hairtail (Trichiurus lepturus), the lebranche mullet (Mugil liza), and the white mullet (Mugil curema). We used five modeling algorithms and 4-7 environmental variables to create ecological niche models, transformed into binary maps for interpretation. We also classified and overlaid Brazilian Marine Protected Areas (MPAs) with the rough-toothed dolphin suitable environments using the MPA Guide. We predicted a 8.7 to 13.6% decrease in suitable areas for the rough-toothed dolphins in Brazil, mainly in the country’s northern and northeastern coast. We predicted a small loss of suitable areas for mullet species (3 to 7%) and a moderate loss for the largehead hairtail (31-35%). To date only 3.7% of rough-toothed dolphin suitable areas overlap with Brazilian MPAs, mainly in low-protection protected areas. Because future loss of suitable areas primarily occurs outside MPAs, they still play a role in mitigating climate change impacts on the species. Our study reveals significant range loss for rough-toothed dolphins and prey in northern and northeastern Brazil because of climate change. Existing MPAs are inadequate, showing an urgent need for expansion.

Two resident populations of Guiana dolphins inhabit the Costa Verde estuarine complex in southeastern Brazil. While these populations are relatively well-studied, little is known of the movement patterns between them. The present study was based on the identification of the individual dolphins that transited between the two Costa Verde populations. Dolphins were photo-identified within the study area between 1994 and 2020, and two photo identification catalogs were compiled based on this material. These catalogs were compared systematically using the finFindR software, which identified 80 individuals that had transited between populations. The most common type of movement was a one-way (no return) movement from Sepetiba to Ilha Grande bay (62.5%).

Climate change harms marine ecosystems, causing habitat loss and shifts in biodiversity. Impacts on vital species like cetaceans disrupt biological communities, emphasizing the need to understand their spatial distribution for biodiversity conservation. Our study assessed potential changes to suitable habitats in Brazil of a key species, the rough-toothed dolphin (Steno bredanensis), and three common prey species (largehead hairtail, Trichiurus lepturus, Lebranche mullet, Mugil liza, and white mullet, Mugil curema) under two climate change scenarios in 2050 (RCP 4.5, mitigated scenario, and RCP 8.5, nonmitigated scenario). We also examined the extent to which Brazilian Marine Protected Areas (MPAs) safeguard the current and future distribution of the rough-toothed dolphin. MPAs were classified and overlaid with species distribution using the MPA Guide tool. We employed five algorithms (MaxEnt, GLM, GAM, RF, and GBM) to calibrate and test current and future ensemble distribution models. Models performance was evaluated using the Area Under the Curve (AUC) test, resulting in continuous and binary maps for interpretation. Models projected a decrease of 23-28% in suitable areas for rough-toothed dolphins, mainly in North and Northeast Brazil. Mullet species would have a 3-5% decline in their habitat, while largehead hairtail would face a 30-31% habitat loss. Only 5% of the rough-toothed dolphin suitable areas overlap with Brazilian MPAs in the current scenario, and 4.4% in both future scenarios. Regarding MPAs considered effective for conservation (fully and highly), the picture is even worse, with less than 1% overlapping with suitable areas regardless of the scenario. While most MPAs do not cover these areas entirely, they can still help mitigate the impacts of climate change on species. These results guide future conservation efforts and emphasize the need for more effective MPAs.