Increase in catch efficiency using a semicircular ground gear in demersal trawls

Abstract In demersal trawls, ground gears are typically fixed to the fishing line to protect against the seabed and ensure seabed contact. Rockhoppers (RH) are among the most applied types of ground gears, especially in fisheries with rough seabed. However, their use has earlier been associated with substantial loss of catch under the fishing line and low catch efficiency. A new ground gear concept known as the semicircular spreading gear (SCSG) has been documented to reduce this loss, but the catch efficiency of RH and SCSG gears has never been directly compared in a systematic commercial scale trial. Using twin trawl configuration, the present study compared the catch efficiency of a RH gear and a SCSG gear with both size selective and blinded trawls. Eighteen hauls were conducted in the Barents Sea demersal trawl fishery where cod ( Gadus morhua ) and haddock ( Melanogrammus aeglefinus ) are target species and redfish ( Sebastes spp.) is an important commercial bycatch species. Using size selective trawls, the catches with the trawl equipped with the SCSG resulted in an average increase of 25.44 for cod, 32.04 for haddock and 64.34% for redfish compared to the trawl equipped with the RH gear. With blinded trawls, the increase changed to 41.35, 65.76 and 44.23% for cod, haddock and redfish, respectively. Despite the significant increase in catch efficiency observed for the trawl equipped with the SCSG, it also caught significantly more undersized fish than the trawl equipped with the RH gear. This increase illustrates the importance of size selective devices, especially if the use of the SCSG is widely adopted by industry.