Comparing Effectiveness of Experimental and Implemented Bycatch Reduction Measures: the Ideal and the Real

Reduction of bycatch is a pressing interest in management of the oceans, and is especially urgent for species which are endangered, threatened, and protected (ETP). A targeted literature review of approaches to reduce bycatch was conducted with an emphasis on fleetwide implementation rather than experimental trials. Our review found few studies that evaluate the success of fleetwide implementation, but rather the bycatch literature is dominated by experimental comparisons of gear modifications with limited assessment of fishery implementation. Those studies that evaluated post-implementation success of bycatch measures focused primarily on ETP species and only two of those included trawl gear (turtle excluders). By far, the most effective methods implemented fleetwide were modified fishing gear and practices, where up to 98% reductions in bycatch were achieved. Individual vessel or fleetwide bycatch quotas, and in some cases area time closures, were also effective. Nevertheless, successful gear modifications were not found for many species or gear types, and in most cases were either not widely adopted or evaluated when implemented. Few evaluations of spatial temporal closures were identified but using data sets on current targeted species catch and bycatch it has been estimated that the least effective approach was large scale permanent no-take areas, where the estimated bycatch reduction would be less than the proportion of fishing grounds closed. Targeted small-scale closed areas were more effective. Real-time closures and individual vessel bycatch quotas appear to be more effective than large permanent closed areas. In the context of how best to protect biodiversity, changes to fishing gear and methods appear to be the most effective, and real time closures hold promise but require intense data collection and management.