Understanding the causes of mortality and contaminant loads of stranded cetacean species in Sardinian waters (Italy) using Bayesian Hierarchical Models

Cetacean strandings represent unique opportunities to collect biological material from these wild animals and obtain information on their population statuses. Here, we apply biological and pathological perspectives to analyze stranded cetaceans collected along the Sardinian coast (Italy) between 2006 and 2011. We quali-quantitatively explore the primary causes of deaths, and use Bayesian Hierarchical Models (BHMs) to explore the potential effects of cetacean sex, age, body length, and month, year, and stranding location on Dicloro Difenil Tricloroetano (DDT) and Polychlorinated Biphenyl (PCB) contaminant loads. Although natural causes, such as bacterial and virus infections, were identified to be the main causes of death among the stranded cetaceans, fisheries also played an important role among the anthropogenic causes of death. The BHMs revealed that both contaminants were positively related to the length, sex and age of the cetaceans, and that higher concentrations of these contaminants were mainly found in larger and older individuals. Despite the scattered nature of these data, the present study contributes valuable insights into the major causes of death of stranded cetaceans, and adds to growing worldwide efforts to biomonitor cetaceans.