Turtles on the trash track: loggerhead turtles exposed to floating plastic in the Mediterranean Sea

Abstract

Loggerhead turtles Caretta caretta spend most of their life in large marine areas occupying a variety of habitats where they are exposed to different types of threats. Among these, marine litter poses a risk of entanglement or ingestion. Areas of risk exposure can be identified where the species overlap with litter accumulations, but gathering data on this highly mobile species and marine litter, especially in high sea areas, is challenging. Here we analysed 5 years of sea turtle and marine litter data collected by a network of research bodies along fixed trans-border transects in the Mediterranean Sea. Ferries were used as observation platforms to gather systematic data on a seasonal basis using standard protocols. Loggerhead turtle sightings over time and space were compared in terms of sightings per unit effort, and risk-exposure areas were assessed based on seasonal overlap of species hot spots and high-density plastic areas revealed by kernel analysis. In almost 180000 km surveyed, 1258 sea turtles were recorded, concentrated mostly in the central Adriatic Sea and Sardinia-Sicilian channels during all seasons, and in the central Tyrrhenian Sea during spring. Plastic comprised the highest fraction of litter items detected. Several areas of higher risk exposure, both permanent and seasonal, were identified, mainly in the Adriatic Sea and during the spring-summer seasons. Records of both species and floating litter were highly variable, underlying the need for continuous long-term monitoring to develop sound conservation and management measures, especially in the identified areas of risk exposure.