acoustic link as used in the simrad trawleye system in the latter case the transmitter of the trawl gauge mechanism drives an electroacoustic transducer being directed from the trawl towards the trawler onboard the vessel the sonar transducer used for fish search or a separate transducer assigned to the trawl gauge may be utilized for receiving the signals from the trawl this transducer feeds the received signals to the receiver 5 fig1 if the sonar transducer is used the sonar associated receiver may of course preferably be used for detecting information from the trawl gauge the pulse trains emitted from the trawl may easily be identified acoustically by the sonar loudspeaker and visually on the sonar recorder when a separate transducer for the gauge is used the signal received may still be fed to the sonar or the echo sounder receiver by suitable switching between the corresponding transducers if the echo sounding receiver is used the gauge transducer may be switched to the echo sounder receiver when the pen of the echo recorder is not touching the paper and a loudspeaker output may then be utilized the trawl gauge will then only provide acoustic indications evidently a separate receiver may alternatively be employed for the trawl gauge and including separate displays which may be acoustic or optical or both if the trawl gauge is connected with the simrad trawleye system the use of displays included in the system will be natural fig7 shows.