Using sound to discourage or distract bycatch species from interacting with fishing gear.
Auditory deterrents are not generally considered useful, except in limited circumstances, in reducing bycatch of seabirds, turtles and sharks. In the main, this is because the feasibility and long-term effectiveness of an acoustic deterrent is affected by habituation (Southwood et al., 2008). This is explained in more detail below.
Bull (2006) describes an acoustic deterrent as any noise used to deter birds from a vessel. Methods used include firing a shotgun, canons, hitting the steel hull, or commercial devices that emit high frequency and loud noises or distress calls (Brothers et al., 1999). However, loud noises frighten seabirds only briefly and at close range (Brothers et al., 1999). Bull (2006) notes that anecdotal observations have reported acoustic deterrents as being effective at temporarily scaring birds away (Crysell 2002). Brothers et al. (1999) suggest that the more often a frightening sound is produced, the less effect it has due to rapid habituation, as with gas guns in agricultural situations. Other commercially available acoustic bird-scaring devices emit high frequency and loud noises or distress calls. These may be effective if used sparingly to avoid habituation (Brothers et al., 1999).
The apparent futility of developing auditory deterrents for seabirds was demonstrated by Brothers et al. (1999) during a trial in which seabirds at a breeding colony were subjected to high-frequency and loud noise as well as distress calls. No detectable response to the sounds was observed.
Southwood et al. (2008) best sum up the potential for auditory techniques to deter sea turtles from interactions with longliners. They found that sea turtles and longline target species are hearing generalists that detect sounds within a similar range**, so any sound generated to prevent sea turtles from interacting with gear would also be detected by, and potentially have a deterrent effect on, target species.
Evidence for marine turtle habituation to auditory deterrents is less clear. Moein et al. (1994) exposed juvenile loggerhead turtles to repeated air gun blasts. Although the loggerheads initially avoided the region where the noise source was located, over a short period of repeated exposure the avoidance response rapidly waned. This change in behaviour may have been due to habituation or to hearing impairment caused by repeated exposure to high intensity sounds.
Barton and Ketten (in Brill et al., 2004) suggested that sea turtles may be attracted to the sound produced by longline floats. They proposed studies to determine the sound spectrum and sound pressure levels produced by both hard and soft floats used in longline fishing.
**Sea turtles and yellowfin tuna are low frequency specialists (Brill et al., 2004), detecting the same low frequency and high energy (i.e. loud) sounds (Swimmer and Brill, 2006).
Little research has been conducted in the area of auditory deterrents and sharks; however, habituation has been demonstrated in sharks, as for seabirds and sea turtles. Recently there has been some interest in using audio attractors to lure sharks away from fishing vessels prior to setting purse seine nets on fish aggregating devices (FADs).
Southwood et al. (2008) in their synthesis of knowledge of acoustic attraction in ocean-dwelling shark species summarised Myrberg (2001, Myrberg et al., 1972, 1976, 1978), as follows: It is generally concluded that sharks, like pelagic teleosts, are low frequency specialists. Silky sharks Carcharinus falciformis and oceanic white-tip sharks Carcharinus longimanis are attracted to low frequency sound within the range of 25 to 1000 Hz, with attractiveness increasing as sound frequency decreases. Irregularly pulsed sounds, such as might be generated by struggling prey, are more attractive than regularly pulsed sounds. Sudden transmission of high intensity sound at close range prompts an immediate and rapid withdrawal in both silky sharks and oceanic white-tip sharks. However, both species rapidly habituate to such signals.
The potential for using audio attractors to lead sharks away from fishing vessels prior to setting purse seine nets on FADs was discussed at a 2009 meeting of the International Seafood Sustainability Foundation (ISSF). Research to determine the feasibility of the different attractors was proposed and issues affecting their success were noted. These included the noisy environment near vessels that may mask attractors and the short period available prior setting to attract sharks away from the FADs. Questions that the research must address were identified. Among these were whether different attractors are needed for different shark species, how the attractors might affect target species, what kind of sounds and at what frequency/beat/ etc should be used, what the range of the sound should be, what platform should be used to distribute the sound and how sound attractors might be used in conjunction with other techniques (e.g. Bait stations).
- Brill, R., Swimmer, Y. and Southwood, A. 2004. Investigations of sea turtle and pelagic fish sensory physiology and behavior, with the aim of developing techniques that reduce or eliminate the interactions of sea turtles with fishing gear in Long, K. and B.A. Schroeder (eds). 2004. Proceedings of the International Workshop on Marine Turtle Bycatch in Longline Fisheries. NOAA Technical Memorandum NMFS-OPR-26.
- Brothers, N.P., Cooper, J. and Lokkeborg, S. 1999. The incidental catch of seabirds by longline fisheries: worldwide review and technical guidelines for mitigation. FAO Fisheries Circular No. 937. FAO, Rome.
- Bull, L. 2006. A review of methodologies aimed at avoiding and/or mitigating incidental catch of seabirds in longline fisheries. WCPFC-SC2-EB-WP-5.
- Crysell, S. 2002. Brigitte Bardot, longlining and Solander fishing. Seafood New Zealand 10:47–49.
- ISSF. 2009. International Seafood Sustainability Foundation meeting on mitigation of by-catches in the tuna purse seine floating object fisheries. Sukarrieta, Spain. Unpublished report.
- Moein, S.E., Musick, J.A., Keinath, J.A., Barnard, D.E., Lenhardt, M. and George, R. 1994. Evaluation of seismic sources for repelling sea turtles from hopper dredges. Report from Virginia Institute of Marine Science, Gloucester Point, VA, to US Army Corps of Engineers.
- 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.
- Swimmer, Y., and Brill, R. (eds.). 2006. Sea Turtle and Pelagic Fish Sensory Biology: Developing Techniques to Reduce Sea Turtle Bycatch in Longline Fisheries. NOAA Technical Memorandum NOAA-TM-NMFS-PIFSC-7.