PAPER Fishing Techniques to Reduce the Bycatch of Threatened Marine Animals AUTHORS ABSTRACT Timothy Werner Unintended injuries and fatalities to non-target marine species—a major component of Scott Kraus “bycatch”—is one of the principal threats to the survival of many endangered marine New England Aquarium populations and species. This paper describes both proposed and existing fishing tech- Andrew Read niques for reducing non-target species bycatch, and reviews their focus across different Duke University 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 develop- Erika Zollett ment. In all, 55 techniques were identified, with the majority directed at reducing bycatch in University of New Hampshire longline fisheries, and intended to benefit primarily seabirds, sea turtles, and small mam- mals. Bycatch reduction is a dynamic field with many examples of effective techniques, though some underserved fisheries and wildlife groups should receive more attention. Introduction illions of dollars are spent each year Methodology some techniques mainly used in aquaculture in the research and development of fishing We attempted to document all available operations became part of the final list. Mtechniques to reduce unintended injuries and information on fishing techniques that have Generally, in categorizing bycatch reduc- fatalities to non-target marine species that forms been used to reduce non-target wildlife spe- tion approaches the tendency was to be inclu- a major component of “bycatch.” The vast cies bycatch in world fisheries. Information sive. For example, Turtle Excluder Devices and majority of this investment in conservation on bycatch reduction methods is highly dif- Sea Lion Excluder Devices were combined as occurs in economically developed countries fuse and for this review we consulted various one approach, under “excluders”, because they (principally the United States, Canada, Aus- sources including journal articles, unpublished fundamentally work the same way. tralia, and Europe) although the problem is government reports, and experts in the field. Both existing and proposed bycatch miti- global in scale. Taken as a whole, bycatch is A number of reviews have examined bycatch gation techniques were considered, and orga- one of the major threats to the survival of many reduction for particular fisheries (e.g., nized according to whether they represented endangered marine populations and species. Broadhurst, 2000; Hall, 1995) or for wildlife an approach (1) intended to avert contact with This paper describes both proposed and groups within particular fisheries (e.g., Gilman a fishing operation and gear altogether, (2) existing fishing techniques for reducing non- et al., 2005), but the scope of this study is all intended to facilitate escape from temporary target species bycatch, and reviews their focus commercial fishing methods and multiple capture, or (3) that required release post-cap- across different fisheries and wildlife groups. wildlife groups. The decision to pursue a more ture. For each technique we identified the fish- The intent of this inventory was to gain a comprehensive treatment was motivated by ing method (gillnet, surrounding net, trap/ better understanding of the range of tech- an interest in identifying bycatch reduction pot, trawl, dredge, and hook-and-line) in niques available and to highlight priorities for approaches that might find application in more which it was or could be used, and identified research and development. than one fishing method, and to better appre- studies undertaken to evaluate its efficacy for The bycatch reduction methods summa- ciate the potential impacts on species or wild- various wildlife groups. The studies compiled rized in this paper are all intended to accom- life groups apart from the one targeted. consisted mainly of ones that directly reported modate continued fishing of target species. Excluded from consideration were recre- on a scientific field trial as opposed to papers Other strategies that can lead to lowered ational fishing, target species bycatch (i.e., ju- summarizing general findings or synthesizing bycatch levels include fishing area closures, venile fish), and strategies for mitigating the responses from fishers. Occasionally, however, temporal closures, reductions in fishing effort, consequences of ghost fishing, a serious and reports of lab studies or third-party papers and cessation of fishing altogether. In some widespread form of bycatch in which fishing reporting on original field research were in- cases, applying one or more of these other gear can continue to catch and kill animals cluded. Wildlife group classifications were se- measures may represent a better strategy for after it has been lost, discarded, or abandoned lected somewhat arbitrarily and represent solving a particular bycatch challenge than by fishers. Depredation, or the predation of broad categories (sea birds, for example) in altering fishing methods, though they often fishing bait or catch by non-target species, order to keep this review at a manageable scale. face resistance from the fishing industry. was considered in this review. This meant that Certainly the number of categories could be 50 Marine Technology Society Journal expanded to include different groups (most Passive acoustic deterrents as sea lions away from a fishing operation. notably non-pelagic fin fish) as well as subsets Objects such as rubber tubes, thick poly- Deterrence may result from noise or tactile of the headings already represented. Never- ester rope, and chains attached to fishing nets annoyance. Anecdotal evidence from some theless, using broad categories of wildlife to alert a marine cetacean to their presence fishermen suggests this practice is widespread groups enables a cursory analysis of the taxo- using echolocation. though its efficacy is not backed up by a num- nomic emphasis in bycatch reduction research ber of studies, and it obviously threatens ani- and implementation of its methods. Vessel noise reductions mal survival. Structural or operational changes to fishing vessels that would decrease the intensity or sig- Quick-release metal wire Description of Techniques nature of their sound output, potentially de- A metal wire attached to an outrigger clip Fifty-five modifications to fishing gear or creasing the degree to which they attract ani- on a troll line. The quick-release mechanism of methods were identified for reducing non- mals that presumably associate these vessels with the outrigger clip causes the wire to travel down target species bycatch. Below is a brief de- a feeding opportunity. At least one study in the the bait line when a fish is captured. The metal scription of each. Those in italics indicate meth- Pacific indicated that the noise from longline wire may deter dolphin depredation (Zollett ods either not yet developed or widely used haulers attracted false killer whales from long and Read, 2006). by the fishing industry that may be undergo- distances (J. Watson, pers. comm.). ing experimental evaluation. Glow rope Animal predation sounds Rope consisting of polypropylene blended Acoustic pingers/alarms Audio recordings of an animal in distress, or with a phosphor that glows a bright yellow-green Underwater sound-emitting devices (maxi- of its predator, played to deter individuals of underwater in wavelengths large cetaceans can mum level of intensity equivalent to approxi- that species from entering into a fishing area. see. It glows for 48 hours after activation at an mately 175 dB re 1 µPa @ 1m) attached to Jefferson and Curry (1996) concluded that this intensity a human can see readily at 20 yards (18 fishing gear, principally gillnets. [Under NOAA’s technique was largely ineffective for reducing m). The design is based on the premise that with Harbor Porpoise Take Reduction Plan for the marine mammal interactions with fishing activ- increased visibility cetaceans and perhaps turtles Gulf of Maine, the sound output intensity for ity based on their review of multiple studies. would be more likely to avoid rope entangle- pingers is stipulated as 10 (±2) kHz at 132 (± ments at night or at depth. Current research is 4) dB re 1 µPa @ 1m (NMFS/NOAA, 1998)]. Metal oxide nets looking at how to maintain the glowing proper- Pingers are now mandated for use in some fish- Nylon nets infused with barium sulfate or ties under the rigors of mechanized hauling. eries in the U.S. Northwest Atlantic, California other metal compounds that have acoustical de- driftnet, and in Europe. The sound of these tection features for reducing small cetacean Bird-scaring devices devices is believed to alert an animal to the pres- bycatch. These may reduce small cetacean and A number of devices used to disturb birds ence of the net and thus decrease the probabil- sea turtle bycatch by increasing the likelihood from foraging on bait. These include stream- ity of entanglement. Although some studies that these animals would “bounce” off the net- ers attached to a pole suspended above the have shown that pingers can have the unin- ting. Experimental results show that they can be area where bait is set or placed in the water, tended consequence of attracting pinnipeds to effective in reducing the bycatch of harbor por- towed buoys, and water jets. fishing operations (Bordino et al., 2002), this poise and greater shearwater (Trippel et al., 2003), may be controllable by raising the emitted fre- though it has not been ascertained if this is be- Dyed bait quency of the pingers above seal hearing (Kraus cause of their acoustic reflectivity, increased stiff- Bait dyed blue to reduce its visibility to et al., 1997). ness, or greater visibility over conventional gillnets. non-target species such as seabirds hovering around longlines as baited hooks are deployed. Acoustic harassment devices (AHDs) Echolocation disruptors Devices that emit sounds of such high Sounds produced to disrupt the normal White mesh on gillnets intensity that they cause pain or alarm in echolocation abilities of cetaceans. Preliminary White mesh panels on the upper part of a certain underwater species.