The use of chemical attractants or deterrents in longline and purse seine fisheries aims to exploit differences in sensory biology between target and non-target species, improving the specificity of fishing and thus reducing bycatch. For example, chemical additives might be used to make longline bait less attractive (or strongly repulsive) to bycatch species or to make it more difficult to locate (by masking attractive odours) . In purse seine fisheries, chemical cues have been used to try and lure sharks away from FADs (fish aggregating devices) . The success of chemical attractants or deterrents in bycatch reduction will depend upon the relative importance of different types of sensory information .
Chemical and other sensory information
Marine animals use a variety of sensory information from their environment to navigate and locate other organisms (prey, predators, and conspecifics) . Chemical, mechanical, visual, and electrical signals (the latter only in the case of elasmobranchs) can be detected by peripheral sensory systems, interpreted by the central nervous system, and result in physiological and behavioural responses . Use of these signals to detect, approach and locate food varies by species (and life stage), distance, prey type and environmental factors [6, 7]. For example, vision is more important to pelagic sharks in locating prey in clear oceanic waters than to coastal sharks hunting in shallow muddy waters. Chemical and acoustic signals propagate furthest from the source, followed by visual, water flow (e.g. currents, topography), and finally electrical information at short range .
Predators often use multiple sensory methods to locate and capture prey, so effective bycatch reduction approaches may involve combinations of strategies simultaneously directed at more than one sensory system. [6,15].
Many gear modifications and deterrents present logistical, economic, and environmental challenges . Chemical deterrents may disperse too rapidly or slowly to be effective, and certain chemicals may pose a pollution risk or could negatively affect marine organisms [9 in 6]. However, chemical deterrents may be cost effective for mass production and relatively simple to integrate into current fishing practices (e.g. pre-treated baits, see ‘SuperPoly Shark’ below) [6, 15]. As mitigation measures in longline fisheries, they might also be practical to enforce as, for example, dockside surveillance could ensure that only treated baits were permitted on longline vessels (electronic monitoring could remove even the need for this). However, no techniques utilising chemical stimuli have yet shown sufficiently widespread effectiveness and practicality that they have been adopted by the fishing industry .
Sharks and Rays
Jordan et al.  reviewed research concerned with bycatch reduction through manipulating elasmobranch sensory biology:
“Sharks display attraction to odours derived from fish and invertebrates (potential prey), particularly those from stressed fish, and repulsion (although variable) to human sweat . Some sharks also display an adverse reaction to chemicals derived from a potential predator  and toxins such as those produced by the moses sole, Pardachirus marmoratus . Hundreds of chemical compounds have been studied as shark deterrents [e.g. 5] yet researchers continue efforts to identify one that is effective across a variety of species. Both synthetic surfactants and semiochemicals (chemical messengers or “clues” sharks may use to orient, survive and reproduce in their specific environments) produced by sharks appear promising [14, 13, 16].”
Studies with shark necromones (semiochemicals extracted from decaying shark tissues) demonstrated that aerosol exposure in the field caused all feeding activities to stop in blacknose and Caribbean reef sharks (Carcharhinus perezi, 16 in 3). However, since sharks are known to feed on other sharks, necromones may in some cases be more attractive than repulsive [6 in 3]. Behavioural reactions to conflicting attractive and repulsive odours may be unpredictable, so future research should also include the use of chemical deterrents with artificial bait .”
‘Super Polyshark’ is an example of a developing bait technology that uses semiochemicals to repel sharks from the hook. Super Polyshark is a time-release pellet, constructed as a paper tube enclosing a polymer infused with a synthetic semiochemical . Tubes are cut into pellets roughly 7.5 cm long. When the pellets dissolve in water they release an odour that repels sharks. According to the manufacturer (SharkDefense), materials used are nontoxic and biodegradable, and target species catch rates are maintained. Both the polymer and the repellent are stable throughout a freeze-thaw cycle, and the repellent dissolves completely within 16 hours of contact with water. The pellet is inserted into the mantle of a squid prior to baiting the hook, or bait can be purchased with the pellets already enclosed. No research has been published to verify the manufacturer’s claims.
Chemical stimuli have also been used in trials to reduce shark bycatch at FADs, though with limited success . Sharks showed mixed reactions to the towing of a bag of bait away from a FAD, with some following a long distance, while others showed no reaction. The FAD remained a very strong attraction stimulus.
Visual and chemical cues attract sea turtles to longline bait but experimentation to date has found that visual responses override chemosensory . For example, sea turtles willingly consumed squid bait that had been treated with naturally occurring defensive compounds (squid and sea hare ink), alkaloids (capsaicins derived from habanero chili peppers), and pungent substances . A recent review found that no noxious chemicals have been identified for successfully reducing sea turtle bycatch . Future research may address differences in sensory biology between species and among life-stages.
There has been some experimentation with olfactory deterrents (fish oils) in demersal longline fisheries [8, 10], with mixed success, dependent on seabird assemblages. Issues identified included the pollution risk of large releases of oil into the marine environment, contamination of seabirds attending vessels and the potential for habituation . Fish oils have not been demonstrated to prevent or reduce seabird mortalities in pelagic longline fisheries .
- ACAP. 2013. Report of Seabird Working Group. Seventh Meeting of the Advisory Committee, La Rochelle, France, 1-3 May. AC7 Doc 14 Rev 1. Includes: Annex 2 ACAP review of seabird bycatch mitigation measures for pelagic longline fisheries; Annex 3 ACAP Summary Advice for Reducing Impact of Pelagic Longlines on Seabirds
- .Clark, E. 1983. Shark repellent effect of the Red Sea Moses sole. In BJ Zahurance, ed., Shark Repellents from the Sea: New Perspectives, Westview Press, Boulder, pp. 135-150.
- Clarke, S., Sato, M., Small, C., Sullivan, B., Inoue, Y. and Ochi, D. 2014. Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures. FAO Fisheries and Aquaculture Technical Paper No. 588. Rome, FAO. 199 pp.
- Dagorn, L. 2011. An update of the EU made project. IOTC-2011-WPEB07-52.
- Gilbert, P.W. 1968. The shark: barbarian and benefactor. Bioscience 18: 946-950.
- Jordan, L.K., Mandelman, J.W., McComb, D.M., Fordham, S.V., Carlson, J.K., and Werner, T.B. 2013. Linking sensory biology and fisheries bycatch reduction in elasmobranch fishes: a review with new directions for research. Conservation Physiology 1(1): cot002. doi:10.1093/conphys/cot002.
- Lokkeborg, S., Siikavuopio, S.I., Humborstad, O.B., Utne-Palm, A.C. and Ferter, K. 2014. Towards more efficient longline fisheries: fish feeding behaviour, bait characteristics and development of alternative baits. Reviews in Fish Biology and Fisheries 24: 985-1003.
- Norden, W.S. and Pierre, J.P. 2007. Exploiting sensory ecology to reduce seabird by-catch. Emu 107(1): 38-43.
- O'Connell, C.P., Stroud, E.M., and He, P. 2013. The emerging field of electrosensory and semiochemical shark repellents: Mechanisms of detection, overview of past studies, and future directions. Ocean & Coastal Management 97: 2-11. doi: 10.1016/j.ocecoaman.2012.11.005
- Pierre, J. and Norden, W. 2005. Trials using shark liver oil to deter seabirds from eating bait during long-line fishing, Leigh, New Zealand. Conservation Evidence 2: 99-100.
- Pierre, J.P. and Norden, W.S. 2006. Reducing seabird bycatch in longline fisheries using a natural olfactory deterrent. Biological Conservation 130(3): 406-415.
- Rasmussen, L.E.L. and Schmidt, M.J. 1992. Are sharks chemically aware of crocodiles? In RL Doty, D Müller-Schwarze, eds, Chemical Signals in Vertebrates IV. Plenum Press, New York, pp. 335–342.
- Sisneros, J. A. and Nelson, D.R. 2001. Surfactants as chemical repellents: past, present, and future. Environmental Biology of Fishes 60(1-3): 117-129.
- Smith, L.J. Jr. 1991. The effectiveness of sodium lauryl sulfate as a shark repellent in a laboratory test situation. Journal of Fisheries Biology 38: 105-113.
- Southwood, A., Fritsches, K., Brill, R. and Swimmer, Y. 2008. Sound, chemical, and light detection in sea turtles and pelagic fishes: sensory-based approaches to bycatch reduction in longline fisheries. Endangered Species Research 5: 225-238.
- Stroud, E.M., O’Connell, C.P., Rice, P.H., Snow, N.H., Barnes, B.B., Elshaer, M.R., and Hanson, J.E. 2014. Chemical shark repellent: Myth or fact? The effect of a shark necromone on shark feeding behavior. Ocean & Coastal Management 97: 50-57.
- Swimmer, Y., and Wang, J.H. 2007. 2006 Sea Turtle and Pelagic Fish Sensory Physiology Workshop. NOAA Technical Memorandum NMFS-PIFSC-12.
- Tester, A.L. 1963. The role of olfaction in shark predation. Pacific Science 17: 145-170.
- WWF. 2014. Super PolyShark.