Western Amazon Basin limits: conservation status and distribution of river dolphins (Inia geoffrensis and Sotalia fluviatilis) in Ecuador.

Authors

Jessica Pacheco-Esquivel, Santiago Varela, Michelle Vela-Torres, Víctor Utreras, Patricio Macas, Mariana Paschoalini, Hugo Trávez, Ismael Fernandez, Jorge Brito

Published in

PeerJ. Volume 14. Pages e21586. Epub Jul 29, 2026.

Abstract

River dolphins (Inia geoffrensis and Sotalia fluviatilis) are apex predators in Ecuador's Amazon, where they face critical endangerment due to their restricted western range limit and escalating anthropogenic pressures. Despite their critical contributions to freshwater ecosystem health, comprehensive population assessments have historically been scarce. Using standardized protocols from the South American River Dolphin Initiative (SARDI), we conducted boat-based surveys spanning 972.6 km across 11 rivers, employing dual-platform distance sampling with habitat stratification. We analyzed 1,141 georeferenced records from Ecuador's National Biodiversity Database, validated through spatial modeling. Density and abundance were estimated using Distance software with satellite-derived habitat areas. Both species exhibited densities substantially lower than those reported for central Amazonian populations, ranging from 0.33-7.61 ind/km² for Inia and 0.05-0.45 ind/km² for Sotalia, consistent with their national Critically Endangered status. We document inter-annual fluctuations in key protected areas while updating known species distributions, confirming Inia in 37 rivers and recording Sotalia in 13 rivers, establishing Ecuador as their westernmost Amazonian range limit. Group sizes varied significantly by habitat, with confluences supporting larger aggregations. This first nationwide assessment reveals acute vulnerability of Ecuador's river dolphins at their distributional edge. The primary value of this work is providing a standardized baseline against which future surveys can detect population changes under increasing anthropogenic pressures. Urgent implementation of Ecuador's Action Plan for river dolphin conservation is needed, prioritizing rivers and confluences with confirmed occurrences, transboundary coordination, and community-based monitoring to prevent local extirpations.

PMID:
42542847
Bibliographic data and abstract were imported from PubMed on 02 Aug 2026.

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