Why study bycatch? An introduction to the Theme Section on fisheries bycatch

Several high-profile examples of fisheries bycatch involving marine megafauna (e.g. dolphins in tuna purse-seines, albatrosses in pelagic longlines, sea turtles in shrimp trawls) have drawn attention to the unintentional capture of non-target species during fishing operations, and have resulted in a dramatic increase in bycatch research over the past 2 decades. Although a number of successful mitigation measures have been developed, the scope of the bycatch problem far exceeds our current capacity to deal with it. Specifically, we lack a comprehensive understanding of bycatch rates across species, fisheries, and ocean basins, and, with few exceptions, we lack data on demographic responses to bycatch or the in situ effectiveness of existing mitigation measures. As an introduction to this theme section of Endangered Species Research 'Fisheries bycatch: problems and solutions', we focus on 5 bycatch-related questions that require research attention, building on examples from the current literature and the contributions to this Theme Section. The questions include: (1) Where is bycatch most prevalent? (2) Which species are taken as bycatch? (3) Which fisheries and gear types result in the highest bycatch of marine megafauna? (4) What are the population-level effects on bycatch species? And (5) How can bycatch be reduced? By addressing these questions, we draw attention to several emerging issues: the importance of artisanal fisheries bycatch, the demographic effects of bycatch, and the need for comprehensive, trans-national mitigation efforts. Although science alone cannot address the complex social, economic, and political factors that contribute to the bycatch problem, this review illustrates ways in which research can contribute to effective bycatch solutions.