First Survey on Sea Turtles’ Interactions in Mussel Farms in Italy

Abstract

Loggerhead turtles (Caretta caretta), opportunistic marine feeders, are increasingly reported as a source of disturbance to mussel farming in the Adriatic Sea. This study combined a survey of Italian mussel farmers with gastrointestinal analyses of stranded turtles along the Adriatic and Tyrrhenian coasts, focusing on Mediterranean mussels (Mytilus galloprovincialis). Sea turtle sightings were most frequent in northern Adriatic regions (Veneto, Emilia-Romagna) during summer and in southern areas (Molise, Puglia) during autumn, likely linked to seasonal water temperatures. Mussels were the most commonly ingested mollusk in the Adriatic, with their presence in turtle diets increasing from 2018 to 2021. While not a primary prey, mussels appear to be a consistent dietary item among turtles due to adaptive feeding. The persistence of such interactions poses management challenges for mussel farms. Broader national and international assessments are recommended to evaluate and mitigate the impact of sea turtles on Mediterranean shellfish aquaculture.

Sea turtles, particularly the opportunistic feeder species loggerhead turtles (Caretta caretta), are increasingly reported as a source of disturbance to mussel farming operations, especially in the Adriatic Sea. Despite the evident damage caused by these interactions, comprehensive national data on the phenomenon are still lacking. This study aimed to address this gap through a survey conducted among Italian mussel farmers, combined with the analysis of gastrointestinal contents from stranded sea turtles along the Adriatic and Tyrrhenian coasts, focusing on the ingestion of Mediterranean mussels (Mytilus galloprovincialis). Survey results revealed frequent turtle sightings in the northern Adriatic (Veneto and Emilia-Romagna) during summer months (June to August), while southern regions (Molise and Puglia) reported more sightings in autumn (September to October), likely influenced by seasonal water temperatures. The Mediterranean mussel was identified as the most commonly ingested mollusk in the Adriatic, with a notable increase in presence from 2018 to 2021. Although mussels are not a targeted prey, they appear to be a consistent dietary component due to adaptive feeding behavior. These interactions are increasingly and consistently reported, leading to significant management challenges for mussel farms. Based on these findings, a broader national and international assessment is recommended to evaluate the overall impact of sea turtles on shellfish aquaculture in the Mediterranean.