SEA TURTLES AND MUSSEL FARMING: RESEARCH SUPPORTING ENVIRONMENTAL POLICY

In recent years, mussel farmers along the Italian coast have reported an unexpected phenomenon: sea turtles moving among the farming lines, often leaving behind damaged nets and clear signs of the shellfish being eaten. These observations prompted the first systematic study in Italy on interactions between Caretta caretta and mussel farming facilities, carried out through a collaboration between the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise, the Università Politecnica delle Marche, ISPRA and CNR-IAS.

Published in the journal Animals , the study combined a nationwide survey of mussel farmers with an analysis of the gastrointestinal contents of stranded or accidentally caught turtles. “This phenomenon brings conservation and aquaculture into direct conversation. - says Dr Ludovica Di Renzo, IZSAM, Laboratory of Aquatic and Terrestrial Ecosystems, Animal Breeding and Experimental Studies Unit - Our aim was to understand how widespread it is, to collect and communicate data, and to offer decision-makers a reliable tool for future planning. The results show that turtle presence in mussel farms is no longer occasional but has increased in recent years, in parallel with rising sea temperatures. This highlights the need to develop mitigation strategies that protect aquaculture activities without compromising sea turtle conservation”.

The questionnaire, completed by 36 mussel farms, revealed that almost all respondents had observed turtles within their farming areas, particularly in the Adriatic Sea. Sightings were more frequent in summer in northern regions and in autumn in the south, following the seasonal pattern of warmer waters. More than 90% of farmers reported direct damage to their structures and product losses, in some cases amounting to tens of thousands of euros.

While mussel farms can act as “biodiversity oases”, attracting a wide range of marine species, interactions with sea turtles can lead to significant economic impacts: torn nets and mussels consumed directly from the ropes may result in losses of up to several hundred thousand euros each year. The deterrent measures tested so far have shown limited effectiveness.

At the same time, analyses conducted on stranded turtles revealed that mussels have become a recurring component of their diet, even though they are not a typical prey item. The frequency of Mytilus galloprovincialis ingestion increased steadily between 2018 and 2021.

“Blue crab (Callinectes sapidus) was also found in the samples, an invasive species that is spreading rapidly in the Mediterranean - adds Di Renzo - and whose presence was still rare at the time of collection. This shows not only how Caretta caretta adapts quickly to a rapidly changing environment, but also how it can act as a sentinel of our seas. Through their presence and diet, turtles reflect the transformations taking place in coastal ecosystems, from new species to warmer waters and increasingly widespread human activities.”

The authors highlight the need for continuous monitoring systems and sustainable mitigation strategies to reduce conflicts between marine wildlife and aquaculture. With their remarkable ability to adapt, sea turtles can become a valuable indicator of the ecological changes occurring in our seas.