On electrical fishing for brown shrimp (<i>Crangon crangon</i>): I. Laboratory experiments

The fishery for brown shrimp (Crangon crangon) in the North Sea is carried out by more than 600 vessels with total annual brown shrimp landings of around 20,000 t. Due to the small mesh size used, the catches also contain large amounts of unwanted by-catch. To find ways of reducing this by-catch, experiments were carried out with electric pulses. The basic idea was to selectively invoke a startle response with shrimp without stimulating any by-catch species. A selective groundrope could then be used in combination with electric pulses to obtain catch separation. As a preparation for sea trials, laboratory experiments were carried out. The pulse generators were tested for their basic characteristics. Experiments were carried out with fish and invertebrate species that are frequently caught in the brown shrimp fishery. The effect of pulse amplitude and frequency in relation to ambient parameters on the response of these animals was tested. To assess the effect of the pulses on these animals, survival experiments were carried out. The main conclusion was that shrimps react strongly to the pulses and most of the other species regularly caught in shrimp trawls do not, so selective electro-fishing has potential. The survival tests indicated that the pulses have no effect on the survival and general behaviour of the animals that have been in the electric field