Each spring, under the cover of darkness and guarded by members of the Italian Coast Guard, 62-year-old Chiara Vigo slips on a white tunic, recites a prayer and plunges headfirst into the crystalline sea off the tiny Sardinian island of Sant’Antioco.

Using the moonlight to guide her, Vigo descends up to 15m below the surface to reach a series of secluded underwater coves and grassy lagoons that the women in her family have kept secret for the past 24 generations. She then uses a tiny scalpel to carefully trim the razor-thin fibres growing from the tips of a highly endangered Mediterranean clam known as the noble pen shell, or pinna nobilis.