Assessment of diet and marine litter in the gastrointestinal tract of loggerhead sea turtles (Caretta caretta) found stranded along Veneto coastline, Northern Adriatic Sea

The loggerhead sea turtle (Caretta caretta) is the most abundant sea turtle specie in the Mediterranean Sea. According to the most recent assessment by the International Union for Conservation of Nature (IUCN), the Mediterranean population is currently classified as Least Concern (LC). Due to the specie’s use of neritic, oceanic and intertidal habitats across different life stages, it is considered as suitable sentinel species for marine pollution and trophic web studies. The presented study investigates the dietary composition of loggerhead turtles, compares methodologies for gastro-intestinal content analysis  specifically macro-identification and eDNA metabarcoding analysis  and assesses the frequency and impact of marine litter ingestion. A total of 111 loggerheads stranded along the Veneto coast were examined, although with a decomposition condition code (DCC) ranging from 1 to 5, leading to different levels of data availability among specimens. Gastro-intestinal content analysis was conducted on 33 specimens via macro-identification, while a subset of 10 of them underwent metabarcoding. Notably, the effectiveness of each method varied depending on the structural composition of the ingested prey. Marine litter was found in 18 individuals, predominantly composed of plastic materials and belonging to the USE SHE category according to the INDICIT consortium protocol (2018). This study provides a first step into the comparison between the methodologies commonly applied in trophic studies, highlighting considerations on their reliability and cost-effectiveness. Furthermore, monitoring marine litter and in particular its association with fisheries is nowadays crucial to better understand and mitigate the anthropological impact on marine wildlife and ecosystem for conservational purposes.