transducer fixed to the trawl headline and linked to a recorder on the vessel by cable or acoustic link. Provides indication of depth of a pelagic trawl,also shows fish above and below the trawl,and i, fish-finder, also called NETSONDE, in commercial fishing, high-frequency sonar device for locating schools of fish. It transmits sound waves downward and receives echoes from the bottom of the sea, or