Since 2016, populations of the Mediterranean fan mussel, Pinna nobilis Linnaeus, 1758, have undergone a dramatic decline throughout the Mediterranean Sea due to recurrent mass mortality events associated with a multifactorial disease. As a result, several conservation initiatives have been launched to support the recovery of this critically endangered species. Among these, the European LIFE PINNA project (LIFE20 NAT/IT/001122) implemented active restoration actions based on the translocation of juvenile individuals collected from larval settlement devices and mussel-farm longlines, together with adult specimens previously maintained for ex situ reproduction.

This study presents the results of a two-year post-translocation monitoring, conducted in the frame of the project action D2, at three pilot sites: the Capo Mortola Marine Protected Area (western Ligurian Sea), the Miramare Marine Protected Area, and the Slovenian coast (northern Adriatic Sea). Between December 2023 and August 2025, 13 translocations were carried out, involving a total of 58 juveniles and 27 adults.

At Capo Mortola, all translocated adults eventually died despite being relocated to a deeper and more sheltered site, although the longest survival exceeded eight months. In contrast, juveniles achieved higher survival rates in the Adriatic Sea. At Miramare, individuals survived in lantern nets for up to six months, while along the Slovenian coast one juvenile survived for 15 months, including one year after transplantation onto the seabed.

Overall, the results highlight marked differences in survival between life stages and study areas. Adult P. nobilis individuals exhibited greater persistence in the Ligurian Sea, whereas juveniles performed better in the Adriatic Sea. The environmental and biological factors underlying these contrasting survival patterns will be investigated within the LIFE PINNA After-LIFE Conservation Plan to support future restoration and conservation strategies for Pinna nobilis.