On Using Electrical Impedance Measurements for Fish Detection in Sea- and Freshwater

Remote fish detection techniques allow to collect data of crucial importance from the point of view of sustainable water resources management. They can also drive development of selective fishing techniques, with minimal ecological impact. Here, we study the possibilities of using electrical impedance measurements for detecting fish in fresh- and seawater environments. We conducted experimental investigations and numerical simulations to determine changes in measured resistance and reactance values due to appearance of a fish in vicinity of electrodes. We used cameras and optical detection as a reference. Electrical impedance measurements allow for short-range remote fish detection, which might be suitable for specific real-life applications. In freshwater, we used parallel strip electrodes to count fish passes in a laboratory tank. The setup was a model of narrow fish passages, which are of great importance for monitoring fish populations e.g. in flowing waters or in aquacultural facilities. In seawater, we used a set of electrodes attached to a dielectric beam and swept over a bottom to detect flatfish partially buried in sand. The detection signal could potentially be used to trigger a startling stimuli in an improved, selective bottom trawling fishing gear. The results demonstrate that fish appearances in the detection regions are manifested by increase of the measured resistance values in freshwater and decrease in seawater. The corresponding reactance values decrease in the both cases. Numerical simulations performed for the freshwater environment using a simplified fish model and generalized electrical tissue characteristics are in fair agreement with the results of measurements, proving to be a valuable tool for supporting design and optimization of the impedance-based fish detection systems.