Stranding records and cumulative pressures for sea turtles as tools to delineate risk hot spots across different marine habitats

Sea turtles are highly mobile species that use oceanic, neritic, and coastal habitats as nursery, foraging, wintering, breeding and migration areas at distant locations throughout their lifetime. Due to their highly migratory nature and large-scale habitat use, they are subjected to multiple threats across marine and coastal ecosystems that can impact every stage of their life cycle and result in increased mortality rates. Here, we present new data on stranding events across the eastern Ionian Sea (central Mediterranean). Our analysis on stranding data, collected over a 6-year period, provided clear evidence of continuing and increased mortality events in the region (n = 413, Caretta caretta: 79%, Chelonia mydas: 4%, and unknown: 17%). Based on the alarming results of increased mortality, and taking into account the limitations posed by the nature of stranding data, we further identified potential risk hotspots within critical marine and coastal sea turtle habitats. To do so, we performed a spatially explicit cumulative pressure assessment at different spatial scales in an effort to identify, map, quantify, and synthesize the multiple anthropogenic pressures that are recognized to potentially impact sea turtles. Our results clearly demonstrated that the Ionian Sea is subjected to intense pressures (i.e. fisheries, marine traffic, and underwater noise). We identified three main hotspots of very high risk related to critical foraging grounds, nesting sites, and migration corridors for sea turtles regardless of the spatial scale of the analysis. We found high sea turtle mortality associated with locations characterized as high and very high risk areas. This study offers key information on mortality and spatial risk for sea turtles that can facilitate their effective conservation. Thus, our findings can be used in the light of marine spatial planning, allowing planners to more realistically assess where conservation resources should be directed to control harmful activities and to mitigate impacts on sea turtles.