Fishing Techniques to Reduce the Bycatch of Threatened Marine Animals

Methodology We attempted to document all available information on fishing techniques that have been used to reduce non-target wildlife species bycatch in world fisheries. Information on bycatch reduction methods is highly diffuse and for this review we consulted various sources including journal articles, unpublished government reports, and experts in the field. A number of reviews have examined bycatch reduction for particular fisheries (e.g., Broadhurst, 2000; Hall, 1995) or for wildlife groups within particular fisheries (e.g., Gilman et al., 2005), but the scope of this study is all commercial fishing methods and multiple wildlife groups. The decision to pursue a more comprehensive treatment was motivated by an interest in identifying bycatch reduction approaches that might find application in more than one fishing method, and to better appreciate the potential impacts on species or wildlife groups apart from the one targeted. Excluded from consideration were recreational fishing, target species bycatch (i.e., juvenile fish), and strategies for mitigating the consequences of ghost fishing, a serious and widespread form of bycatch in which fishing gear can continue to catch and kill animals after it has been lost, discarded, or abandoned by fishers. Depredation, or the predation of fishing bait or catch by non-target species, was considered in this review. This meant that some techniques mainly used in aquaculture operations became part of the final list. Generally, in categorizing bycatch reduction approaches the tendency was to be inclusive. For example, Turtle Excluder Devices and Sea Lion Excluder Devices were combined as one approach, under “excluders”, because they fundamentally work the same way. Both existing and proposed bycatch mitigation techniques were considered, and organized according to whether they represented an approach (1) intended to avert contact with a fishing operation and gear altogether, (2) intended to facilitate escape from temporary capture, or (3) that required release post-capture. For each technique we identified the fishing method (gillnet, surrounding net, trap/ pot, trawl, dredge, and hook-and-line) in which it was or could be used, and identified studies undertaken to evaluate its efficacy for various wildlife groups. The studies compiled consisted mainly of ones that directly reported on a scientific field trial as opposed to papers summarizing general findings or synthesizing responses from fishers. Occasionally, however, reports of lab studies or third-party papers reporting on original field research were included. Wildlife group classifications were selected somewhat arbitrarily and represent broad categories (sea birds, for example) in order to keep this review at a manageable scale. Certainly the number of categories could be M Introduction illions of dollars are spent each year in the research and development of fishing techniques to reduce unintended injuries and fatalities to non-target marine species that forms a major component of “bycatch.” The vast majority of this investment in conservation occurs in economically developed countries (principally the United States, Canada, Australia, and Europe) although the problem is global in scale. Taken as a whole, bycatch is one of the major threats to the survival of many endangered marine populations and species. This paper describes both proposed and existing fishing techniques for reducing nontarget species bycatch, and reviews their focus across different fisheries and wildlife groups. The intent of this inventory was to gain a better understanding of the range of techniques available and to highlight priorities for research and development. The bycatch reduction methods summarized in this paper are all intended to accommodate continued fishing of target species. Other strategies that can lead to lowered bycatch levels include fishing area closures, temporal closures, reductions in fishing effort, and cessation of fishing altogether. In some cases, applying one or more of these other measures may represent a better strategy for solving a particular bycatch challenge than altering fishing methods, though they often face resistance from the fishing industry.