Translate the following English sentence to French:
"It must also be said that 'clearing ballast' at sea is unfortunately to a very great extent exempt from the charging system. Only inspections at sea and more frequent inspections of vessels docking in ports would be likely to reduce the amount of dumping at sea."
Il convient également de dire que le "déballastage" en mer est malheureusement très largement indépendant du système de taxation : seuls des contrôles en mer et des contrôles plus fréquents de la flotte faisant escale seraient susceptibles de limiter les rejets en mer.