The tucuxi (Sotalia fluviatilis) is a small dolphin found only in the Amazon River and most of its tributaries (da Silvaand Best, 1994). It is one of the seven species deemed to be representative of the serious threats affecting small cetaceans around the world: bycatch in fisheries, habitat destruction, and direct capture (Avila et al., 2018; Taylor et al., 2020). Tucuxi and Amazon River dolphins (Inia spp.) are included in the Conservation Management Plan (CMP) for South American River Dolphins, endorsed in 2020 by the International Whaling Commission, to promote the conservation of river dolphin species (Trujillo et al., 2021).

For the tucuxi, scarce information is available about life history, abundance, population connectivity, and the spatial extent of threats and local population trends. One localized study documented a drastic population decline consistent with a Critically Endangered listing (da Silva et al., 2018), but the 2020 IUCN Red List assessment, that lacked information on population structure and threat distribution, designated the species as Endangered (da Silva et al., 2020). Analysis of both mitochondrial and nuclear DNA from 55 tucuxi tissue samples from locations across the Colombian, Peruvian and Brazilian Amazon showed evidence of population connectivity between the western and eastern Amazon (Caballero et al., 2018), but it lacked sufficient power to resolve population structure. Tucuxi are difficult to biopsy and capture is not recommended due to probable capture myopathy.

The aim of this project is to evaluate the feasibility of using environmental DNA (eDNA) collected from water where these dolphins are found, to obtain genetic information needed to elucidate population structure so that threats to isolated subpopulations can be identified and addressed. This key knowledge gap needs to be filled to facilitate development of integrated conservation plans and implementation of mitigation measures within the CMP being developed by the range states (Brazil, Colombia, Ecuador and Peru).