Marine Mines
Used to destroy the ships and the boats. They harm the local fishers the most.
A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, any vessel. Naval mines can be used offensively, to hamper enemy shipping movements or lock vessels into a harbor; or defensively, to protect friendly vessels and create "safe" zones.