Evaluating a large-mesh belly window to reduce bycatch in silver hake (Merluccius bilinearis) trawls

Abstract

Small-mesh trawls targeting silver hake (Merluccius bilinearis) in Northeastern USA are managed as exemptions to the northeast multispecies management plan. These exemptions require that the catch of regulated groundfish species is less than 5% of the total catch weight for small-mesh gears targeting silver hake. At present, only a raised footrope trawl (RFT) or drop-chain-only trawl (DOT) (in New England, it is specifically called “sweepless trawl”) in conjunction with a Nordmøre-style grid can be used to land silver hake with small mesh off the coast of Maine. The historical Maine silver hake fishing grounds have a very rugged bathymetry that makes the use of these modified groundgears difficult, if not impossible. This study tested a trawl with and without a large-mesh belly window (LMBW) using a traditional rockhopper footrope for 58 tows and reduced the bycatch of red hake (Urophycis chuss) and aggregated bycatch. There was no significant difference in the predicted mean catch of silver hake between trawls (although the LMBW trawl had a 13.50% reduction). Additionally, there was no difference in catch for commercial-size silver hake (>20cm) between the two trawls. Both video and length analysis determined that small silver hake were caught less frequently by the LMBW trawl. These results indicate that a small-mesh trawl employing a LMBW can effectively be used to commercially target silver hake off Maine (USA), replace the requirement of a RFT or DOT, and maintain the less than 5% regulated groundfish requirement.