Comparison of Catches between Selective and Conventional Otter Trawls for a Coastal Fishery

Abstract

New selective trawl fishing gear have been developed by fishers, administrators, and researchers to mitigate the bycatch and discard problem in a coastal trawl fishery in Choshi, Chiba, in eastern Japan. As a result, the selective fishing gear that has a two-level codend with the Bycatch Exclusion Window (BEW) at the top panel of the upper-bag was developed. We discuss the performance of this selective fishing gear in practical fishing conditions from the results of trials in which the selective and the conventional gears were compared in normal operations. We compared tow, catch and landing data during 21 cruises and there were significant differences in mean towing duration and mean sorting duration (time needed to sort catch, in each haul) between the selective and the conventional fishing gears. Decrease of towing duration is considered an increase in handling labor and a decrease in sorting duration as successful catch separation. Significant differences were not observed in catch amounts and landing values for total and major target species in the trial for such species as swimming crab (Ovalipes punctatus) and several species of flatfish. On the other hand, significant reductions in catch amount and/or landing value were observed for minor target species: dragonets (Callionymidae), common Japanese conger (Conger myriaster) and Japanese whiting (Sillago japonica). These species have long and thin bodies that easily pass through meshes of BEW. Southern rough shrimp (Trachypenaeus curvirostris) and ocellated octopus (Octopus ocellatus) are small-sized target species, and catch reductions were expected. However, catch amounts and landing values for both species were not decreased in the selective fishing gear. Separation of marine debris from the catch by the selective fishing gear enabled the avoidance of incidental discarding and quality damage caused by contacts with debris. Fishers decided to use this selective fishing gear beginning in autumn of 1998 as acceptable economic impact of the selective fishing gear was confirmed from this trial.