Reducing bycatch in beam trawls and electrotrawls with (electrified) benthos release panels

Abstract

Benthos release panels (BRPs) are known for their capacity to release large amounts of unwanted benthos and debris, which can decrease mortality on these animals and eases the on board sorting process aboard demersal beam trawlers. They can reduce the bycatch of undersized fish, which is desired once the European discard ban is implemented. However, unacceptable commercial losses of sole (Solea solea L.) and damage to the BRP as a consequence of suboptimal and unsuitable rigging in the traditional beam trawl with chain mat, is hampering a successful introduction in commercial beam-trawl fisheries. To eliminate these drawbacks, square-meshed BRPs with different mesh sizes (150, 200, and 240 mm) were rigged in a trawl with square net design as used in electrotrawls and tested for selectivity. In addition to this, the effect of electric stimulation at the height of the BRP to eliminate the loss of commercial sole was examined. According to our observations, no abrasion of the net attributable to suboptimal rigging occurred in any of the BRPs tested. The catch comparisons showed significant release of benthos and undersized fish in all panel mesh sizes, but there was always a significant loss of marketable sole in the 150, 200, and 240 mm BRPs. Adding a 80 Hz electric cramp stimulus to the BRP, resulted in equal catches of sole larger than 25 cm as the standard net, without negatively affecting the release of benthos and most undersized commercial fish. This clearly demonstrates the promising potential of electrified BRPs (eBRPs), but further optimization by using smaller BRP mesh sizes or optimized electric stimuli is warranted to retain all marketable sole.