Biological and ecological traits rather than geography control mercury (Hg) in scutes of marine turtles from the Southwest Atlantic.

The use of sentinel species in monitoring programs for toxic metals such as mercury (Hg) is essential to understand these pollutants' impact on the environment. For this purpose, it is essential to use organisms that have a lifespan compatible with the residence time of Hg in the oceans, and preferably with a wide geographical distribution, such as sea turtles. Here, we assess the regional variability of Hg concentrations using carapace scutes of four sea turtle species along the foraging and spawning area in the northeast coastline of Brazil. Mercury concentrations in samples showed no relationship with the environmental Hg levels (obtained from literature). Rather, Hg concentrations varied according to species-specific biological, and ecological traits. Characteristics such as the ontogenetic shift in the diet of Chelonia mydas, capital breeding in females, depth of foraging in oceanic waters, and selectivity of food items, such as in Eretmochelys imbricata, significantly influenced Hg concentrations.

On the brink of isolation: Population estimates of the Araguaian river dolphin in a human-impacted region in Brazil.

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.