Aerial survey of manatees, dolphins and sea turtles off northeastern Brazil: Correlations with coastal features and human activities

•405 animals were sighted, comprising 41 manatees, 78 dolphins and 286 turtles.•Manatees showed a positive correlation with sea turtles, and both with motor boats.•Dolphins and sea turtles presented higher densities in MPAs with reef environments.•MPAs with well-preserved mangrove estuaries presented higher densities of manatees. The objective of the present study was to analyze the distribution of manatees, dolphins and sea turtles off northeastern Brazil through aerial surveys, relating them to specific habitats and human activities, with emphasis on marine protected areas (MPAs). Surveys were conducted between January and April 2010 at 150m altitude and 140kmh−1, using two independent observers. Strip transects were flown in a zigzag pattern. Transects covered 4026km in more than 27 flight hours. A total of 36 sightings of manatees (Trichechus manatus manatus, 41 individuals), 28 of dolphins (Delphinidae, 78 individuals, including 10 Sotalia guianensis) and 256 of sea turtles (Cheloniidae, 286 individuals) were recorded. Manatees and sea turtles displayed solitary habits, while dolphins were commonly seen in groups. Manatees were positively correlated with sea turtles, probably due to their preference for sheltered shallow habitats with favorable conditions for foraging and resting. Furthermore, manatees showed a positive relationship with mangrove estuaries, and medium-sized coastal cities probably due to the intense urban development in many estuarine areas. Manatees and sea turtles were also positively correlated with boats, showing a severe threat for these species. Density of manatees was significantly higher within MPAs with preserved mangrove estuaries than in non-protected areas, while dolphins and sea turtles were observed in high densities MPAs with coral reefs. The elevated density of these organisms shows the vital importance of protecting and adequately managing unique ecosystems to ensure a sustainable future for the populations of severely threatened species.