Modified otter trawl legs to reduce damage and mortality of benthic organisms in North East Atlantic fisheries (Bay of Biscay)

Abstract

Despite a consensus about the significant damages to marine benthos and commercial fish stocks induced by mobile fishing gear, the extent and intensity of this practice have currently grown all over the world. The main problems of fisheries management are the capture and killing of juvenile and undersized fish and thus restrictions mainly concern mesh size in cod-end. However another recurrent problem and non-negligible is the by-catch of undersize commercial fish and of non-target species. Hence, regulations to reduce such by-catch have formed a part of fisheries management techniques since the early 20th century. As a consequence, successful developments and technical modification have been used to reduce capture of undersized fish and discards (i.e. mesh size, separator panels, and sorting grids) in the last decades. Technical modification concerning reduction of damage and mortality to benthic communities are less documented. Most of the tentative to replace tickler chain, panels or legs by other systems have failed, while results showed a decrease in non-target catch, and a decrease in commercial catch was observed. This paper presents fishing experiments with modified otter trawl aimed at reducing discard rates and direct mortality of benthic infauna and epifauna without affecting the level of landings (i.e. a comparison of environmental effects caused by a conventional otter trawl compared to a modified otter trawl with enlighten experimental legs). Catch composition, by-catch and short-term effects to macro- and megafauna communities of both fishing gear (conventional and modified) were investigated. Results show that no differences for commercial catch biomass or for benthic communities' structure were observed. Moreover, by-catch analysis showed no difference while significant higher damage and direct mortality were observed for target and non-target species caught by the normal otter trawl compared to those caught by the modified one. Consequently, although limited, the severity of the damage appears to be linked with the type of trawl-legs used. The modified otter trawl permits to decrease damage and mortality to captured and non-captured organism and thus to reduce impacts to exploited marine ecosystems. These results are of interest and appear attractive in the framework of marine ecosystems preservation and conservation, as well as of fisheries management.