Population parameters of Guiana dolphins ( Sotalia guianensis ) in a southern Brazilian estuary

Populations of many coastal cetaceans are threatened by negative anthropogenic impacts. Key precursors to effective recovery plans include understanding life histories and population parameters to establish baselines for subsequent changes. Here, we provide this information for one of the largest populations of Guiana dolphins ( Sotalia guianensis ), in the Paranaguá estuarine complex (PEC), southern Brazil. Between 2014–2015 and 2017–2018, photo-identification data were collected from vessels at two locations bordering a (i) marine conservation zone and (ii) port area in the PEC to estimate population parameters via mark-recapture modeling. Group sizes varied between 1 and 41 animals at both locations, and a Jolly–Seber mark-recapture model estimated total abundances to be 454 (95% CI = 287–718) and 902 individuals (95% CI = 652–1247), respectively. Calves were identified in 62% and 71% of groups. There was also location-specific variability among the probabilities of capture (0.43; 95% CI = 0.21–0.67 vs 0.94; 95% CI = 0.91–0.96) survival (0.77; 95% CI = 0.31–0.95 vs 0.26; 95% CI = 0.23–0.30) and individuals entering populations (0.00–0.23 vs 0.00–0.26). These differences were attributed to various geographic and anthropogenic factors in the PEC. By providing regional baseline abundance of Guiana dolphin population dynamics and their spatio-temporal use, this study supports future local assessments of population trends, and facilitates broader between-population comparisons for better assessing population risks and the conservation status of the species. Collectively, the results reinforce the need for (i) existing regional protected areas, and (ii) ongoing systematic surveys to inform managing anthropogenic activities along the southern Brazilian coast, and other areas with multiple and cumulative impacts on coastal dolphins.