The rollerball net: A new approach to environmentally friendly ottertrawl design

Few attempts have been undertaken to reduce the benthic by-catch or the potential damage of demersal fishing gears on the benthic environment and specifically on invertebrate species. With this in focus, a modified otter trawl was designed with the aim of reducing ground contact while simultaneously maintaining commercial catch landings. The basic concept incorporates modifications to the foot rope where rollers have been added as a stimulation system for raising fish, as well as a drop out square mesh panel in the bottom sheet allowing for the release of benthic organisms collected by the net. Preliminary sea trials undertaken in Galway Bay, Ireland compared the performance of the modified trawl to that of a standard gear. Commercial catch landings were not affected by the rollerball design but benthic invertebrate discards and debris material were reduced by 32 and 66% respectively. The catch composition of the fish component did not differ between the two designs for any species. The towing force required to drag the rollerball design was 12 % less than that of the standard gear. In addition, the commercial catch was independently assessed and found to be cleaner and less silted in the rollerball net suggesting that this design did not penetrate into the seabed to the extent of its counterpart. More extensive research on this gear modification is recommended before further conclusions can be drawn.