Fishers’ local ecological knowledge reveals human dimensions of the Araguaian river dolphin, an endemic and threatened megafauna species in the Brazilian Amazon

Aquatic mammals are ecologically important apex predators that regulate aquatic food webs but are increasingly threatened by multiple anthropogenic pressures. Improving knowledge of threatened species is therefore essential to support effective conservation. We employed fishers’ local ecological knowledge (LEK) to investigate the conservation and human dimensions of the Araguaian river dolphin ( Inia araguaiaensis ) in the Tocantins–Araguaia Basin. We conducted 120 interviews across seven localities to document ethnotaxonomic classification, feeding ecology, fisheries interactions, traditional uses, and perceived population trends. Fishers distinguished 12 ethnotaxa and identified 16 ethno-species as prey. They also reported widespread negative interactions with fisheries, including net damage, depredation of captured fish, and fish dispersal, although only 32% reported incidental captures. Occasional medicinal and spiritual uses of dolphin body parts were also recorded. 49% of interviewees perceived populations to be increasing, whereas 31% perceived declines. Perceived increases were associated with the absence of deliberate killing and the species’ life-history traits, whereas perceived declines were linked to reduced prey availability and environmental degradation. Our results demonstrate that LEK provides robust, place-based information that can complement long-term monitoring, improve understanding of socioecological systems, and support participatory conservation strategies. Collectively, these findings highlight that recognizing fishers as key knowledge holders and integrating LEK into decision-making are fundamental to developing effective conservation and management strategies for threatened river dolphins and freshwater biodiversity.