Symposium Abstract: Reducing Seabed Contact of Bottom Trawls
Typical bottom trawls leave tracks when they are towed over the seabed due to trawl doors and bobbins, or other roller gears in contact with the seabed. Reducing contacting points of doors or bobbins can reduce tracks left by trawls and impact of trawling on benthic system. Footgear or sweep of a bottom trawl may consist large steel bobbins in order to roll over rough grounds to protect netting from damaging. We examined if the number of bobbins on an offshore shrimp trawl was necessary for maintaining trawl geometry and stability, and preventing the gear from damaging when fishing for shrimps off Newfoundland and Labrador. Through flume tank tests, we were able to balance a commercial shrimp trawl when the number of bobbins was reduced from the original 31 to nine. Reducing the number of bobbins on the footgear also reduced drag of the trawl by 12%, resulting in savings on fuel. Preliminary sea trials indicated that the trawl with less number of bobbins on its footgear may result in the footgear intermittently being lifted off bottom, but this may not necessarily result in reduction in catch of shrimps. The trawl rigged with less bobbins on its footgear was more likely to incur damage when fishing under rough sea and seabed conditions. We are continuing the project in Newfoundland and in New England with the concept of semi-pelagic shrimp trawls with either trawl doors off the seabed while leaving the trawl on the bottom, or with the bottom-contacting trawl doors and a offbottom “sweepless” trawl.