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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 (25° 03′ S, 47° 55′ 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 population 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.
Key Words: abundance, mark-recapture, robust design, photo-identification, Guiana dolphins, Sotalia guianensis
Page Numbers: 56-65