Hazardous seascapes for marine turtles in the Mediterranean sea

Abstract

This research advances our understanding of the prevalence and impact of recognised anthropogenic threats to sea turtles in their environment. Using Multiscale Geographically Weighted Regression (MGWR), this study examines spatial distribution of marine hazards (i.e., floating marine litter and density of fishing vessel routes) and their association with sea turtle mortality in the waters surrounding the islands of Sicily and Sardinia, in the western basin of the Mediterranean Sea. The aim is to identify regions of heightened ecological risk, herein defined as hazardous seascapes, to support targeted conservation and mitigation efforts. The potential distribution of offshore mortality was estimated using a numerical backtracking model of sea turtle carcass drift based on 5-years (2019-2023) of stranding events. Mortality areas were found to spatially overlap with regions of dense fishing vessel routes. In contrast, this relationship was less pronounced when considering the broader and more diffuse distribution of debris across the study areas. MGWR provided a quantitative characterization generating a predictive statistical model for hazardous seascapes, where sea turtle mortality hotspots were associated to the combined influence of marine litter and fishing vessel routes. Selected models explained 87 % and 83 % of the variance for the investigated marine regions, respectively. Covariates linked to marine litter show consistently positive effects in a broad coastal belt, roughly the first ∼30 km offshore, indicating elevated risk nearshore. In contrast, covariates tied to fishing-route density vary more sharply in space, with pronounced peaks around major ports, but with a narrower coastal footprint than litter.