Dear Marmamers, just sharing that a new paper on abundance estimates of Guiana dolphins (*Sotalia guianensis*) in the Cananeia estuary, southeastern Brazil, is now available. Cheers, Prof. Marcos Cesar de Oliveira Santos Laboratorio de Biologia da Conservacao de Mamiferos Aquaticos (LABCMA) Instituto Oceanografico, Universidade de Sao Paulo Mello, AB; Molina, JMB; Kajin, M & Santos, MCO 2019. Abundance estimates of Guiana dolphins (*Sotalia guianensis*; Van Bénéden, 1864) inhabiting an estuarine system in southeastern Brazil. *Aquatic Mammals* 45(1): 56-65. ABSTRACT: Baseline demographic information is essential for effective conservation and management strategies for most living species. The abundance of Guiana dolphins (Sotalia guianensis) is poorly known, yet species conservation is considered a high priority in areas where human activities may induce population declines. This study estimated abundance for Guiana dolphins in the Cananeia estuary (25o03' S, 47o55' W) in southeastern Brazil using mark-recapture data and Pollock’s Robust Design Model. Systematic boat-based photo-identification surveys were based on data collected in the summer and winter of 2015 and in the summer of 2016. A total of 55 capture events allowed identification of 133 different individuals. The best model indicated a popula- tion with random temporary emigration, a time-constant survival rate, and heterogeneous time-varying capture probabilities among primary periods. The temporary emigration rate (γ’’= γ’) was 0.05 (± 0.03). Estimated population sizes were 430 (95% CI: 410 to 451) individuals in the summer of 2015, 384 (95% CI: 366 to 403) individuals in the winter of 2015, and 414 (95% CI: 392 to 438) individuals in the summer of 2016, indicating that environmental variables among seasons may have a mild effect on the estimated size of this surveyed population. These estimates should stand as an important baseline for future comparisons. Systematic, long-term monitoring of this population is recommended, and is required to accurately assess population trends.