# Elucidating Sexual and Spatial Influences on the Trophic Ecology of Amazon River Dolphins (Inia geoffrensis) and Mercury Contamination

## TL;DR

This study explores how mercury contamination and diet vary in Amazon River dolphins, influenced by sex and location, highlighting conservation concerns.

## Contribution

The study reveals sexual and spatial differences in trophic ecology and mercury exposure in Amazon River dolphins.

## Key findings

- Males showed greater niche plasticity while females maintained consistent feeding strategies.
- Spatial segregation between males and females/juveniles drives mercury concentration differences.
- Narrower isotopic niche areas suggest reduced prey availability and habitat degradation risks.

## Abstract

The Amazon Basin hosts an immense biodiversity, including
the endemic
Amazon River dolphin (Inia geoffrensis). Dietary exposure to mercury (Hg) is one of the threats to this
top predator species. This study investigated the relationship between
Hg exposure, trophic position and foraging areas in I. geoffrensis. We analyzed Hg concentrations and
stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in 111 blood samples collected in different years.
The Hg concentrations ranged from 23 to 582 μg/kg wet weight,
while mean δ13C and δ15N values
were −29.6 ± 1.7‰ and 9.8 ± 0.5‰, respectively.
Narrower isotopic niche areas were observed in the latest year analyzed,
suggesting reduced prey availability and/or restricted foraging areas.
Males displayed greater niche plasticity, whereas females maintained
consistent feeding strategies over time. Spatial segregation between
males and females/juveniles appeared to be the main driver of differences
in Hg concentrations. These findings raise concerns for species conservation
under the increasing frequency of extreme Amazon droughts, which can
alter Hg dynamics and degrade habitats. Monitoring I. geoffrensis health is essential not only for the
protection of this endangered species, but also as a sentinel for
Hg exposure risk in the Amazonian human population, mainly riverine
and indigenous communities.