Use acoustic devices at aquaculture systems
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 6
Background information and definitions
Acoustic devices may be used to deter marine or freshwater mammals from aquaculture systems. These are high power devices that operate by emitting sounds of an intensity and frequency that are aversive to the target mammal species. The primary aim has usually been to reduce mammal predation on fish stocks and damage to gear (therefore reducing human-wildlife conflict), although the risk of mammal entanglement may also be reduced. However, the high intensity sounds produced by acoustic devices have the potential to cause hearing damage to target species (Götz & Janik 2013). Negative and far-reaching effects have also been reported for non-target marine mammal species, such as killer whales and harbour porpoises (Johnston 2002, Morton & Symonds 2002, Olesiuk et al. 2002). The use of multiple acoustic devices within an area has the potential to cause significant noise pollution (Findlay et al. 2018).
Findlay C.R., Ripple H.D., Coomber F., Froud K., Harries O., van Geel N.C.F., Calderan S.V., Benjamins S., Risch D. & Wilson B. (2018) Mapping widespread and increasing underwater noise pollution from acoustic deterrent devices. Marine Pollution Bulletin, 135, 1042–1050.
Götz T. & Janik V.M. (2013) Acoustic deterrent devices to prevent pinniped depredation: efficiency, conservation concerns and possible solutions. Marine Ecology Progress Series, 492, 285–302.
Johnston D.W. (2002) The effect of acoustic harassment devices on harbour porpoises (Phocoena phocoena) in the Bay of Fundy, Canada. Biological Conservation, 108, 113–118.
Morton A.B. & Symonds H.K. (2002) Displacement of Orcinus orca (L.) by high amplitude sound in British Columbia, Canada. ICES Journal of Marine Science, 59, 71–80.
Olesiuk P.F., Nichol L.M., Sowden M.J. & Ford J.K.B. (2002) Effect of the sound generated by an acoustic harassment device on the relative abundance and distribution of harbor porpoises (Phocoena phocoena) in Retreat Passage, British Columbia. Marine Mammal Science, 18, 843–862.
Supporting evidence from individual studies
A site comparison study in 2001–2003 of 27 Atlantic salmon Salmo salar farms in the North Atlantic Ocean, off the coast of Maine, USA (Nelson et al. 2006) found that using acoustic devices did not reduce numbers of fish lost or damaged due to Western Atlantic harbour seal Phoca vitulina concolor predation. Estimated numbers of fish lost or damaged due to seal predation did not differ significantly between farms that did or did not use acoustic devices (data reported as statistical model results). There was also no significant difference between farms that used acoustic devices seasonally or all year round, or those that operated them for different numbers of hours/day. Eighteen farms used acoustic devices for 8–24 h/day (12 all year round; six seasonally). Nine farms did not use acoustic devices. Farm managers were sent annual questionnaires in 2001–2003. Data were collected on methods used to deter predators and estimated numbers of fish lost or damaged due to seal predation.Study and other actions tested
A before-and-after, site comparison study in 2007–2008 at two salmon farms in the Reloncaví fjord, Chile (Vilata et al. 2010) found that installing an acoustic device reduced the amount of Atlantic salmon Salmo salar predated by South American sea lions Otaria flavescens, and fewer salmon were predated overall compared to at a farm without a device. At one farm, lower amounts of salmon were predated by sea lions in April–June 2008 after the acoustic device was installed (total 8 tons) compared to April–June 2007 before the device was installed (total 13 tons). During April–June 2008, lower amounts of salmon were also predated at the farm with the acoustic device than at a second farm without a device (total 68 tons), where amounts of predated salmon increased during this time (from 8 to 42 tons/month). The amount of predated salmon at the two farms did not differ significantly in January–March 2008 before the device was installed (8 vs 13 tons). An acoustic device (Airmar dB Plus II with eight sound projectors) was installed at one of two salmon farms in March 2008. The device emitted 1.4 ms sounds at intervals of 40 ms and a frequency of 10.3 kHz. Data on salmon predated by sea lions in 2007–2008 were taken from each of the two farms’ logbooks.Study and other actions tested
A before-and-after study in 2009 at a fin-fish farm in the Mediterranean Sea, off the coast of Sardinia, Italy (López & Mariño 2011) found that an active acoustic device did not reduce common bottlenose dolphin Tursiops truncatus presence, approach distances, group size or time spent in the area compared to before or after the device was active. Bottlenose dolphin presence and minimum approach distances did not differ significantly before, during or after the acoustic device was active (data not reported). The same was true for average dolphin group sizes (before: 2 dolphins; during: 5 dolphins; after: 3 dolphins) and the average time dolphins spent in the area (before: 15 minutes; during: 19 minutes; after: 23 minutes). In February–June 2009, an acoustic device attached to a fish cage was activated (emitting 1.2–1.8 second tones at 6.2–9.8 kHz) for 40 minutes during each of 144 trials. The fish farm (12,000 m2) consisted of 21 floating nylon mesh cages, 200 m from the shore. During each trial, dolphins were observed from a stationary boat during 40-minute periods before, during and after the device was active. Thirty periods for each of the three stages (before, during, after) were randomly selected for analysis.Study and other actions tested
A controlled study in 2007 at a fish farm in the North Atlantic Ocean, Scotland, UK (Götz & Janik 2015) found that using an acoustic device reduced the number of harbour seals Phoca vitulina that approached a fish cage. Overall, fewer seals approached within 250 m of the cage when an acoustic device was used (2 seals) than when a device was not used (17 seals). No significant difference in numbers of approaches was found at distances of 250–1,500 m (with device: 8 seals; without: 11 seals) or >1,500 m from the cage (with device: 8 seals; without: 7 seals). Sixteen experimental trials (with an acoustic device) and 16 control trials (without a device) were carried out. Each trial lasted an average of 3.5 h. The device (an underwater loudspeaker emitting 200 ms pulses with a peak frequency of 950–1,000 Hz) was placed on a fish cage with the transducer at a depth of 17 m. Seals were tracked with a theodolite from the shore during each of the 32 trials in June–July 2007.Study and other actions tested
A before-and-after, site comparison study in 2010–2012 at a salmon Salmo salar farm in the North Atlantic Ocean, Scotland, UK (Götz & Janik 2016) found that deploying an acoustic device reduced predation on caged salmon by grey seals Halichoerus grypus and harbour seals Phoca vitulina. Fewer salmon were lost to seal predation while an acoustic device was deployed (0–70 fish/month) compared to before (97–104 fish/month) or after (4–9 fish/month) the device was deployed or at two control sites without acoustic devices (2–238 fish/month; 0–99 fish/month). No seal predation occurred during 10 of 12.5 months in which the acoustic device was deployed, whereas seal predation occurred during each of eight months at one control site without an acoustic device and six of seven months at the other. From January 2011 to February 2012, an acoustic device with 2–4 transducers (emitting 200 ms pulses at random intervals) was deployed at the centre of a salmon farm comprising a grid of 2 x 4 rectangular steel cages. Control sites were two salmon farms (with two rows or grids of 6–9 cages) without acoustic devices. In 2010–2012, salmon losses to seal predation (dead fish with bite wounds) were counted during 2.5 months before, 12.5 months during and 3 months after the acoustic device was deployed and during 7–8 months at the two control sites.Study and other actions tested
A before-and-after study in 2011 at a salmon Salmo salar farm in the North Atlantic Ocean, Scotland, UK (Götz & Janik 2016) found that deploying an acoustic device reduced predation on caged salmon by grey seals Halichoerus grypus and harbour seals Phoca vitulina. Fewer salmon were lost to seal predation while an acoustic device was deployed (0–10 fish/cage) compared to before the device was deployed (27–72 fish/cage). In May 2011, an acoustic device with a single transducer (emitting 200 ms pulses at random intervals) was deployed at a salmon farm (two rows of nine cages). Two cages on the farm were stocked with fish. Salmon losses (dead fish with bite wounds) were counted and removed from each of the two cages every 6–8 days during four weeks before and two weeks after the acoustic device was deployed.Study and other actions tested