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.