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

Abstract

Understanding environmental and anthropogenic variables that influence the presence of dolphins in coastal areas is fundamental for conservation planning and forecasting. In this study, we applied generalized additive models to identify areas of 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. Models were built using 70% of the data to test the model and 30% to evaluate its predictive performance. Variables investigated included depth, slope, seabed complexity, and distance to the coast, breakwaters, and the fishing grounds. The best model explained 40.8% of the total deviance. Seabed complexity, distance to the breakwaters and distance to the fishing grounds were the most important variables, with dolphins showing a preference for areas with a less complex seabed immediately adjacent to the breakwaters (<500 m, decreasing with distance) as well as a preference for fishing grounds (again decreasing with distance). Using the validation data, the model showed excellent performance. The habitat use and preference of Guiana dolphins in the study area seem to be mainly influenced by foraging opportunities, 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.