Abstract: The invention consists of a method which comprises a plurality of steps for determining difference in distance from a reference point to at least two sensor modules 10, 20 that are located under water. The sensor modules 10, 20 comprise means for sending and receiving acoustic signals to each other and to a hydrophone 30 at the reference point. Connected to the hydrophone 30 is a calculating unit 40 that utilises arrival time of the received signals from the sensor modules to determine difference in distance from the sensor modules 10, 20 to the reference point.

Abstract: A method for determining distance between a vessel and at least one sensor module arranged on fishing gear being towed by the vessel, the at least one sensor module comprising a transmitter connected to a clock and a receiver connected to a clock being arranged on the vessel, comprises time-synchronising the clocks connected to transmitter and receiver with each other, transmitting a series of signals from the transmitter at a predetermined fixed time interval, receiving in the receiver the signals from the transmitter, and, on the basis of the time of the reception of the signals, calculating the distance between the transmitter and the receiver.

Abstract: A trawl sensor device for monitoring trawl doors and the distance of the trawl to the boom during trawling operations comprises at least one acoustic transmitter and receiver, the transmitter being adapted to be positioned such that an acoustic signal is transmitted towards the seabed at a forward-pointing angle, and means for communication between the sensor device and a vessel. The transmitted acoustic signal is reflected from the seabed and is received at this position and the distance between the acoustic transmitter and the seabed is calculated based on the difference in time between transmission and reception of the acoustic signal and the forward-pointing angle.

Abstract: A system for control of trawling comprises two or more sensors for measuring trawl parameters during fishing, a processor unit for processing sensor data, a screen for displaying sensor data and/or processed sensor data. A method for control of trawling comprises measuring two or more trawl parameters during fishing, calculating the trawl parameters' deviation from desired value, and displaying the deviation on a screen.

Abstract: The invention consists of a method which comprises a plurality of steps for determining difference in distance from a reference point to at least two sensor modules 10, 20 that are located under water. The sensor modules 10, 20 comprise means for sending and receiving acoustic signals to each other and to a hydrophone 30 at the reference point. Connected to the hydrophone 30 is a calculating unit 40 that utilises arrival time of the received signals from the sensor modules to determine difference in distance from the sensor modules 10, 20 to the reference point.

Abstract: A system and method for sorting fish where the system comprises;—a trawl (2) consisting of at least one trawl bag (3, 3?, 3?), and where the at least one trawl bag (3, 3?, 3?) has an opening which covers a part of an inflow area in the trawl (2),—at least one monitoring device (6) arranged in connection with the inflow area and where signals can be transmitted to a processing unit from the at least one monitoring device (6), and—where a device, based on data from the processing unit, can move the opening in the at least one trawl bag (3, 3?, 3?) to a position where fish flow through the inflow area but on the outside of the at least one trawl bag (3, 3?, 3?).