Populations of freshwater dolphins are declining in response to increased human pressure, including habitat degradation, overfishing, bycatch, poaching and obstruction of free-flowing river corridors by dams. At least three river dolphin species occur in South America: the Amazonian river dolphin, or boto (Inia geoffrensis), the Bolivian river dolphin (Inia boliviensis) and the tucuxi (Sotalia fluviatilis). A fourth species, the Araguaian boto (Inia araguaiaensis), been proposed for the Tocantins-Araguaia, a large river basin in northern Brazil. Here we show that the Araguaian boto population in the Tocantins River is relatively small (N = 1083, CV = 0.52). During a survey to estimate density and abundance, 138 groups (198 individuals) of botos were observed along a ~600 km stretch of the Tocantins River in five different habitats (river margin, river channel, channel, island margin, and a dam reservoir). Overall, lower densities of the Araguaian boto were registered downstream of the Tucuruí dam, the world’s fifth largest hydropower dam. Density was 68% lower in the river margin habitat downstream (0.23 ind./km², CV = 0.92) than upstream (0.72 ind./km², CV = 0.53). In addition, density within the Tucuruí reservoir decreases from upstream areas towards the dam. Geographic post-stratification of data into sub-regions (downstream, reservoir, upstream) in relation to the Tucuruí dam helped to reduce CV by ~70%, which illustrates the high variability in the encounter rate in these areas. Our findings suggest that the Araguaian boto population has been impacted by the construction of the Tucuruí dam. The construction of other dams proposed for the Tocantins-Araguaia basin should be planned strategically to minimize overlapping with the Araguaian boto distribution. Coordinated conservation actions are imperative to prevent the Araguaian boto from reaching extinction or near-extinction as some of their Asian counterparts such as the Yangtze, Ganges, and Indus river dolphins.

The dolphins Inia geoffrensis—boto and Sotalia fluviatilis—tucuxi are threatened cetaceans inhabiting river ecosystems in South America; population numbers are still lacking for many areas. This paper provides density and abundance estimations of boto and tucuxi in 15 rivers sampled during the past nine years as part of a multinational research alliance. Visual boat-survey data collection protocols and analyses have been developed since 2012 (based on Distance Sampling methods) and recently reviewed (2019) to improve robustness and comparability. Differences across the sampled rivers and the analyzed river basins (Amazon and Orinoco) pointed to a density/population size gradient with lower densities and abundances observed in the Orinoco basin (0.9–1.5 ind./km²), passing through the eastern Amazon basin (2–5 ind./km²), and the largest numbers found at the central Brazilian Amazon (lower Purus River—2012 (14.5 boto/km², N = 7672; 17.1 tucuxi/km², N = 9238)). However, in other parts of the central Amazon, the density of dolphins was smaller than expected for high productive whitewater rivers (1–1.7 ind./km² in the Japurá and Solimões rivers). We attributed these differences to specific features of the basin (e.g., hydro-geomorphology) as well as to the cumulative effects of anthropogenic activities.

In Brazil, the Amazon River dolphin or boto (Inia geoffrensis) is considered a charismatic creature of the Amazonian culture and freshwater biodiversity, which attracts a lot of tourists searching for unique experiences with wildlife. Under several threats, boto’s population is declining and opportunities/alternatives to develop conservation actions are needed, advised, and urgent. This study aimed to investigate from local riverside perspective if the dolphin-watching Community-Based EcoTourism (CBET) is a good conservation alternative for boto. By applying semi-structured interviews and participant observation methods, we studied the perception of 68 riverside people from the Mamirauá Sustainable Development Reserve (MSDR), central Amazon. Some 88.3% of respondents considered the dolphin-watching tourism as an important conservation measure, since it helps in the dissemination of local knowledge about the species, restrains ‘outsider’ fishermen presence, and generates alternative income to communities. The same respondents understand as important the conservation of boto, and 68% said that keeping ecological relations between animal and environment helps in the conservation of its habitats. The economic benefits of dolphin-watching tourism in the MSDR were reported by 32.8% respondents. Community-based wildlife tourism is one of the widely used tools to promote species conservation and their habitats, when following good practices and promoting awareness, economic benefits, and scale up impacts. The results from this study provide information which may support strategies for the touristic management and conservation of botos in the Amazon.

River dolphins of the genus Inia are strongly influenced by seasonal hydrological dynamics, yet information on Inia araguaiaensis remains limited. We investigated spatial and seasonal patterns of dolphin occurrence along a 240 km stretch of the middle Araguaia River (Brazil) during the dry (100 transects) and wet (91 transects) seasons. Boat-based transects were used to estimate sighting rates and the number of individuals per sighting. We applied a Generalized Linear Model (GLM, quasi-Poisson) to test for seasonal differences in group size and a Generalized Linear Mixed Model (GLMM, Tweedie distribution) to evaluate variation in sighting rates. No significant effect of season was detected on group size, although slightly higher values were observed during the rainy period. On the other hand, sighting rates were significantly higher in the rainy season. Channel depth and width had no effect. These results likely reflect atypical hydrological conditions, highlighting the importance of interannual variability when interpreting seasonal patterns.

River dolphins in South America face critical threats including illegal hunting for bait, accidental bycatch, mercury pollution, habitat fragmentation from dams, and extreme droughts driven by climate change. Consequently, species such as Inia geoffrensis and Sotalia fluviatilis have been recategorized as endangered following decades of consolidated monitoring in the Amazon and Orinoco basins. To address this crisis, political advocacy led to the South American Action Plan (2010-2020) and the implementation of national management plans in Brazil, Colombia, Bolivia, Peru, Ecuador, and Venezuela. These efforts are supported by the River Dolphins Initiative SARDI, a consortium of organizations that leads and generates data on dolphin abundance and threats to guide science-based policy decisions. At a global level, conservation has advanced through the Conservation Management Plan (CMP) of the International Whaling Commission and the Global Declaration for River Dolphins (2023), which seeks to halt population declines and protect critical habitats. Furthermore, river dolphins have been integrated into international treaties like the Ramsar Convention, which recognizes them as indicator species for the health of freshwater ecosystems. However, the sources highlight that effective implementation is hindered by legal asymmetries between countries—such as differing regulations on the piracatinga fish trade—as well as weak governance in the Amazon basin, illegal transboundary trade, and institutional instability during government transitions. Long-term survival depends on a strategic alignment of national policies and international commitments to address these threats at the regional scale where they occur.

River dolphins (Sotalia fluviatilis and Inia spp.) rely on sound for navigation, foraging, and communication, making passive acoustic monitoring a promising research tool. We present a preliminary assessment of the PODs detections across five South American countries. A total of 486 816 minutes of recordings were collected, with 18% showing positive detections. Detection rates varied among sites and were generally higher in confluences, lakes, and in a dam reservoir than in other habitats. Although PODs cannot reliably distinguish among sympatric species and may miss weak signals, our results show that they can provide useful information on dolphin occurrence in remote freshwater systems, supporting their use as a complementary tool for broad-scale monitoring.