Locks on the ile de Ré

Since Medieval times there have been locks which are fishing areas around the lle de Ré where the sea is surrounded by containing stone walls.  The locks break the swell of the tide and protect the shore.  However, there are only about 12 left on the island when at the beginning of the century there were about 140. Building these is an irreplaceable maritime art and took up to between 10,000 and 20,000 man hours as well as the the continual and ongoing maintenance involved.   The stone is naturally fragile without cement.  Of course the removal of oysters from the stones also causes damage.  ADEPIR is a Society for the Protection of these locks and evidently one can volunteer one's services to help maintain the locks. Certain people have fishing licences and rights to collect the fish from these locks.