Sonars and sonar systems for fish finding, trawl sonars, echo sounders, echo sounder transducers, echo sounders and echo sounder systems for use in combination with marine positioning systems; sensors for catch control, namely, battery powered sensors mounted on the fishing gear, namely, catch-, depth-, temperature, trawl height-, trawl door spread-, trawl geometry, trawl mounted echo sounders, sensor measuring pitch, roll and yaw; marine radars; VHF-radios; marine communication radios; marin...