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Habitat use of Guiana dolphin (Sotalia guianensis) in a heavily urbanized embayment

Ana Carolina Oliveira de Meirelles*, Katherine Fiedler Choi-Lima, ThaĆ­s Moura Campos Vila Nova, Emygdio Leite de Araujo Monteiro Filho, Tito Monteiro da Cruz Lotufo

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ABSTRACT: Understanding environmental and anthropogenic variables that influence dolphins’ presence in coastal areas is fundamental for conservation planning and forecasting. In this study, we applied Generalized Additive Models to identify areas of a high probability of occurrence of Guiana dolphins in Mucuripe embayment, a heavily urbanized area in northeastern Brazil. Sighting and effort data were collected during systematic, boat-based surveys between 2009 and 2011. Seventy percent of the data were used to test the data and 30% to evaluate the model's predictive performance. Variables investigated were depth, slope, seabed complexity, distance to the coast, breakwaters, and the fishing ground. The best model explained 40.8% of the total deviance. Seabed complexity, distance to the breakwaters and to the fishing ground were the most important variables, with dolphins showing preference for areas with less complex seabed, immediately adjacent to the breakwaters (<500 m), decreasing with distance, and in the fishing ground, decreasing with distance. The model performance using the validation data showed excellent performance. The habitat use and preference of Guiana dolphins in the study area seem to be mainly influenced by foraging opportunity, with dolphins concentrating in areas with higher prey abundance and where foraging success is higher because of a strategy called ’barrier-feeding’, in which animals herd fish against piers, breakwaters, and the coast.