Testing of a helix twine off-bottom trawl on Georges Bank

Abstract

The massive biomass of Eastern Georges Bank haddock (Melanogrammus aeglefinus) is difficult to harvest without capturing less robust, but still valuable groundfish stocks like Atlantic cod (Gadus morhua) and some flatfish species. Specialized haddock trawls that raise the mouth of the nets off-bottom have reduced bycatch but the very poor status of Atlantic cod prioritizes even greater reduction to prevent exceeding regulatory fishing quotas. Raising the entire fishing gear off-bottom may further reduce bycatch while eliminating benthic impacts, expanding access to grounds previously off-limits to bottom-tending trawls. We evaluated an off-bottom trawl (OBT) to harvest Eastern Georges Bank haddock while reducing catches of overexploited stocks. The OBT net has very large meshes at the front end, made with innovative “helix” twine that produces lateral hydraulic forces while towing, resulting in self-spreading of the meshes. We established optimal gear configurations to achieve the target OBT net shape and distance to the seafloor by using an assortment of mensuration sensors/loggers and cameras. The OBT caught similar amounts of haddock and reduced some bycatch more than a standard bottom “Ruhle trawl”, but also caught fish of the same lengths despite the OBT using a smaller mesh-sized codend. The OBT also demonstrated similar requirements in vessel RPMs as the Ruhle trawl, despite having a larger swept area.