Flatfish pulse fishing - Research results and knowledge gaps
Knowledge about the effects of pulse fishing is spread out over various reports and policy documents; a complete and accessible overview of knowledge is lacking. Pulse fishing is relatively new: in this fishery, fish are caught by means of electric pulses. Those pulses cause muscle contractions in fish, resulting in them being released from the sea bottom and caught in the net. Because the pulse technique is relative-ly new and because electric fishing is not permitted in Europe, the development of this fishery brings up a lot of questions. The fishery study group Pulse and SumWing (part of the fishery study group Flatfish) asked IMARES and LEI to make a summary of the available knowledge on the effects of pulse fishing and of lacking knowledge. This report summarises effects on landings and discards, effects on the ecosystem, management of the fishery and CO2 emission. At the end of the report, we give an overview of knowledge gaps.
An important observation is that the results of the studies may not be comparable amongst each other. The conditions under which the studies were carried out may differ. This complicates drawing firm con-clusions about ‘the’ effects of ‘the’ pulse fishery. Instead, we draw conclusions on the effects that were measured under specific conditions. We came to the following conclusions:
- Cod and whiting: chance of fractures in spinal column of large cod;
- Dogfish: minimal effects (no mortality or change in behaviour besides muscle contractions), alt-hough effects on the functioning of electro receptors was not studied;
- Benthic invertebrates: some species did not respond to pulse (for example spisula and starfish); other species did (razor clam, shrimp, green crab and rag worm). Observed effects were reduced survival rates and food uptake;
- Marketable plaice and sole: the pulse gear catches similar amounts of marketable sole as the con-ventional beam trawl, but lower amounts of marketable plaice;
- Plaice and sole quality & survival: these species with pulse trawl are less damaged and have a higher chance of survival than plaice and sole caught with conventional beam trawl;
- Discards: less discards for all species categories that are discarded;
- Fuel consumption: pulse trawl has a lower resistance than the conventional beam trawl, resulting in reduced fuel consumption and C02 emission.
Despite the large number of studies that have been carried out, several topics need more investigation:
- Indirect (or: delayed) mortality;
- Long term effects on species that encounter pulse trawl gear and on their populations;
- Non-mortal effects;
- Effects on reproduction;
- Minimum and maximum values for pulse characteristics (is there a ‘safe range’?)
- Effects of pulse fishing on first life stadia of marine organisms that reproduce in shallow water;
- Effects on substrate and water column: can use of pulse result in toxic matter?
International scientists stated that control and enforcement issues should be resolved before the number of vessels using pulse trawls is increased. In 2012 procedures for control and enforcement were devel-oped, but they are not being used yet.