Western Amazon Basin limits: Conservation status and distribution of river dolphins (Inia geoffrensis and Sotalia fluviatilis) in Ecuador
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 exhibit critically low densities (Inia: 0.03–6.53 ind./km²; Sotalia: 0.04–1.13 ind./km²), confirming national critically endangered status. We document population declines 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. 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.