Estimation of distribution, density, and abundance of franciscana dolphins (Pontoporia blainvillei) in FMA-Ia (Espírito Santo, Brazil) using passive acoustic monitoring (PAM)

Abstract

The franciscana dolphin (Pontoporia blainvillei), recently subdivided into the distinct subspecies P. b. pukusi in Espírito Santo, Brazil, is one of the most threatened cetaceans in South America. Conventional visual surveys are limited in its turbid, nearshore habitat, highlighting the need for alternative approaches. This dissertation develops a stepwise framework for passive acoustic density estimation (PADE). Chapter 1 defines biologically meaningful acoustic groups using clustering of echolocation click trains. Chapter 2 calibrates acoustic footprints by pairing passive acoustic detections with drone counts, enabling group-size estimation. Chapter 3 integrates these advances to provide the first abundance and trend estimates for P. b. pukusi in FMA-1a (2019–2022). Surveys covered 4,562 km, yielding 224 click trains aggregated into 71 clusters. Nearly all detections were concentrated near the Doce River mouth, while the northern stratum showed minimal occurrence. Annual abundance estimates ranged from ~1,150 to ~1,300 individuals, indicating a small, spatially restricted, and possibly declining population. This work demonstrates the feasibility of PADE for small coastal dolphins and provides critical baseline data for the conservation of P. b. pukusi.