Range-wide monitoring reveals demographic vulnerability in Lahille's bottlenose dolphins

Robust demographic estimates are critical for effective conservation but often lacking for threatened species, demanding long-term, range-wide monitoring to generate data and assess risk. Here, we quantify key demographic parameters and evaluate extinction risk at a metapopulation scale to inform conservation planning for Lahille's bottlenose dolphin, an endangered dolphin endemic to the coastal waters of the Southwest Atlantic Ocean. Using Robust Design mark-recapture models on data from a coordinated photo-identification program (2018–2023) across five Management Units (MUs) in the southern Brazil-Uruguay subpopulation, we estimated abundance and survival. Best estimates indicate a total subpopulation abundance of 341 individuals (95% CI: 333–348), with annual survival varying among MUs from 0.934 (95% CI: 0.856–0.971) to 0.968 (95%CI: 0.926–0.986). Metapopulation-based Population Viability Analysis (PVA) projects a 2% decline in subpopulation size over three generations (63 years) under current conditions, with ~4% extinction risk for two MUs. Under a worst-case scenario with increased bycatch and habitat degradation, a 94% decline in the subpopulation is projected. Findings highlight the vulnerability of Lahille's bottlenose dolphins and the urgent need for habitat protection and bycatch mitigation. We recommend maintaining and expanding coordinated, long-term monitoring to support adaptive management.