Therefore , many countries demand that all mining operations be planned on land and records kept so the mines can later be recovered more easily .
Each mine is recorded for later clearing , but it is not unusual for these recordings to be lost together with the ships .
Many countries demand that all mining operations be planned on land and records kept so the mines can later be recovered more easily .
Each mine is recorded for later clearing , but it is not unusual for these recordings to be lost together with the ships .