3 Acoustic Deterrents in Capture Fisheries
3.1 Nature of the Interactions
There is a long history and extensive literature on the issue of marine mammal depredation on, and bycatch in, capture fisheries (Northridge, 1984; Northridge, 1991; Wickens, 1995). Pinnipeds are widely reported to interact with fishing operations practically everywhere the two overlap (Wickens, 1995). Many cetacean species also interact with fisheries in a variety of detrimental activities as well as some mutually beneficial ways. Problems from the fishery perspective include depredation - the removal of fish from nets - and damage to fishing gear. Problems from the perspective of the marine mammals include bycatch and injurious retaliation from fishermen.
Konigson (2006) categorised depredation type interactions in much more detail using as her template interactions between grey seals and static net fisheries in the Baltic. These are reproduced below:
Losses due to seal attacks
Visible and direct losses
- Damaged catch
- Damage to fishing gear
Invisible direct losses
- Catch removed completely from the fishing gear
- Fish scared away from the fishing area
Indirect losses due to damaged fishing gear
- Loss of catch due to damaged fishing gear
- Costs of new material
- Time spent repairing fishing gear
- Reduced life of the fishing gear
Indirect additional losses
- Increased time and fuel consumption due to checking and hauling the fishing gear more often
- Longer fishing trips to areas where there is less seal interference
- Lost fishing opportunities, due to both fishing grounds and fishing gear not being worth using any more as a result of seal interference
The same list would apply in many other situations, including those involving cetaceans. Damage to fisheries by cetaceans includes the depredation of longline fisheries by killer whales, sperm whales ( Physeter macrocephalus) and other large toothed cetaceans (Hamer et al., 2012), and damage to coastal gillnet and trammel net fisheries by bottlenose dolphins (Bearzi, 2002; Read, 2008) among some other species.
Bycatch is recognised as being the single greatest conservation threat to marine mammals globally, with (very crudely estimated) annual totals of over 300,000 cetaceans and a similar number of pinnipeds drowning in fishing gear globally (Read et al., 2006).
Within Scotland, gillnet fishing is limited to a small number of vessels, but bycatch and depredation are recorded from such fisheries nonetheless ( SMRU unpublished data). Seal bycatch has also been recorded to a limited extent in trawl fisheries in Scotland, while damage by seals is widely reported in trap net (bag net) fisheries for salmon, and in salmon rod and line fisheries, where the mere presence of seals in the vicinity of rod and line fishing can be enough to reduce catches to zero. As a consequence, seals are shot under licence at river fisheries and at netting stations, with 225 having been reported shot in such circumstances during 2012  .
Although there has as yet been no comprehensive assessment of seal bycatch in Scotland or in the UK, published estimates for South-Western waters (England and Wales) suggest an annual take of several hundred (mainly grey) seals in static net fisheries.
Globally, there has been a great deal of attention devoted to the use of acoustic deterrent devices in attempts to minimise both depredation and bycatch involving marine mammals. This research can best be examined by focusing on the broad fishery type.
Dawson et al. (2013) have provided a recent review of efforts to minimise both bycatch and depredation in gillnet fisheries. The authors tabulated 28 acoustic deterrent devices from 12 different manufacturers, a few of which are now no longer being marketed. These devices are primarily used to minimise bycatch of cetaceans, but at least seven of these devices have also been tested as potential deterrents of depredation by cetaceans. Most of these devices are relatively low powered, use alkaline, lithium-ion or rechargeable batteries, and are designed to be small enough to hang from a gillnet. Such devices are generally referred to as 'pingers' (See section 1.3)
Some 19 controlled experiments were reviewed by Dawson et al. (2013), in which the use of pingers was tested in nets fished against control sets without active pingers. Fourteen of these trials were targeted at reducing harbour porpoise bycatch, and in all but three of these there was a clear reduction in porpoise bycatch. In three experiments either no bycatches were observed at all, or pingers showed a degree of mechanical failure. In five other studies pingers were shown to reduce bycatch of common dolphins ( Delphinus delphis) and other pelagic cetaceans: striped dolphins ( Stenella coeruleoalba), franciscana ( Pontoporia blainvillei) and bottlenose dolphins. Bycatches of common dolphins were reduced in two fisheries, as were those of beaked whales and franciscanas. Bycatch rates of striped dolphins were lowered in a controlled experiment in the Mediterranean, but did not continue at the low rate shown in the experiment once pingers were more widely used in the fishery in an extended trial. Bycatch rates of bottlenose dolphins were not significantly reduced in the final study, but the sample size was small. Evidence from a variety of other trials suggests that bottlenose dolphin bycatch cannot easily be reduced using pingers, and that some pingers may have the opposite effect of arousing an antagonistic reaction in this species. Overall, the review concludes that pingers appear to work well with shy and neophobic species but are less likely to succeed with species like bottlenose dolphins that appear to be bolder.
Pingers have also been used to try to reduce bottlenose dolphin depredation of set nets in seven experimental trials. Some of these have shown limited reductions in net damage or fish removals, but the results overall have been inconsistent and unconvincing, and Dawson et al. (2013) point out that they were unaware of any fisheries in which fishermen have been using such devices voluntarily for any significant length of time in order to address the issue of dolphin depredation. Two other unpublished pinger studies were identified that had resulted in no effect on depredation by cetaceans.
Pingers are generally considered ineffective in minimising seal depredation of gill nets, and there is more concern that pingers deployed to minimise cetacean bycatch may end up increasing pinniped depredation. Such effects have been demonstrated in Argentina (Bordino et al., 2002) for South American sea lions ( Otaria flavescens) and for grey seals in Sweden (Stridh, 2008). Carretta and Barlow (2011) found an increase in sea lion entanglement and an increase in depredation after pingers had been introduced to the California driftnet fishery for swordfish and sharks, but found this was most likely not due to the pingers themselves but to other factors including increasing sea lion numbers. They also noted a decrease in elephant seal ( Mirounga sp.) bycatch after pingers became mandatory.
Marine mammal interactions with longlines also include both bycatch and depredation. Hamer et al. (2012) have reviewed the records of cetacean entanglement and depredation in such fisheries, and they report at least 15 cetacean species either depredating or becoming caught in longline fisheries. In higher latitudes where demersal longlines are most common, sperm whales and killer whales are the species most frequently involved. In lower latitudes where pelagic longlining for tuna is common, false killer whales and pilot whales ( Globicephala spp.) are most frequently recorded. In at least two cases Hamer et al. (2012) state that there is evidence of cetacean population declines (for a false killer and a pilot whale population) as a result of these interactions. Losses to fisheries have been estimated in a couple of locations as running into several thousand dollars per day per vessel. In some areas fishing is no longer economically viable and fishing is diverted away from areas of high depredation.
Unsurprisingly, given the high economic costs involved, several companies market or plan to market acoustic deterrent devices intended to minimise whale depredation of longlines. Tests of such devices are limited. Mooney et al. (2009b) tested one device (Savewave) with a captive false killer whale ( Pseudorca crassidens) in Hawaii. They found that the device initially disrupted the animal's ability to detect targets, but that the device became less effective with time. A new version of this device is now marketed by Savewave as the Orca Saver  , but there appear to be no independent tests of its efficacy.
Nishida and McPherson (2011) tested two STM products (Dolphin Dissuasive Device, or DDD and Dolphin Interactive Dissuasor, or DiD) in the Japanese longline fishery in the Pacific where they were attempting to prevent toothed whale depredation (mainly by killer whale and false killer whale). Preliminary results suggested that both devices 'probably' caused a reduction in depredation.
We are aware of at least two other companies that intend to market, or are already marketing, acoustic deterrent devices to longline fisheries  &  . The effectiveness of these devices and this approach remains untested.
|KG No.||Knowledge Gap|
|36||Efficacy of devices designed to deter depredating odontocetes in capture fisheries is currently unknown.|
Interactions between large whales and static gear including fish-traps and creels are well known from many parts of world, where substantial mortalities may occur. Early research in this area was undertaken in Newfoundland by Jon Lien, who was one of the pioneers of acoustic deterrence. Lien and colleagues showed that a prototype pinger could be used to minimise humpback whale ( Megaptera novaeangliae) collisions with fish traps (Lien et al., 1992).
Acoustic alarms (pingers) have been used by the Queensland Shark Control Program ( QSCP) since 1992 (Erbe and McPherson, 2012) and are also used in other Australian states as well as South Africa to prevent both dolphin and whale entanglement. It is as yet unclear how effective these devices have been, with conflicting reports in the literature due in part to the low background rates of entanglement of just a few animals per year (McPhee, 2012). Several devices have been trialled, including a newly marketed device, the Fumunda/Future Oceans 3 kHz whale pinger, which is intended to work at frequencies aligned to humpback whales' peak hearing sensitivities. Promotional material from future oceans  suggests this device is effective, though we have yet to see the results of any independent trials  .
|KG No.||Knowledge Gap|
|37||Efficacy of low frequency devices for deterring baleen whales is unknown.|
|38||There is general lack of understanding of the response of marine mammal species to different signal-types and how these responses are modified or mediated by context.|
3.3 Use of Seal Scarers in Capture Fisheries
Seal scarers similar to (or in some cases the same as) those used in fin-fish aquaculture have been used by some other marine industries, including wild capture fisheries, to try to limit seal depredation. These have all been louder devices than the pingers discussed above. Acoustic deterrent devices used in these circumstances tend to require large amounts of power, necessitating either mains electric or generator supply, or the use of large lead-acid batteries. Such devices are problematic to deploy directly in the open sea. At least one manufacturer advertises their product as being effective at deterring seals and sea lions, as well as cetacean species, from trawl and longline fisheries  . The Lofitech ADD has also been trialled, with some success, as a predator deterrent in salmon fisheries of the UK and Sweden ( e.g. Graham et al., 2009; Konigson, 2006; Westerberg et al., 1999).
Conflicts between pinnipeds and salmonid fisheries in America have driven the development and testing of several different anti-predator devices/techniques, some of which may have application elsewhere. The original research and development for the "sealchaser" by Oregon State University was largely intended for the defence of salmon hatcheries and wild salmon stocks returning to spawn. Migrating fish, restricted by structures such as locks and dams, were found to be particularly vulnerable to pinniped attacks (Mate et al., 1986a). Between 1980 and 1984 the device was tested at three study locations. This device was found to have a significant effect in reducing the number of foraging seals at three study sites.
A report in Mate and Harvey (1986) by Andrew Rivinus found a device to be effective for around two years when used to protect a fish ladder and salmon release facility in Yaquina Bay, Oregon. Few details were reported, but after two years of apparently no interactions, seal activity in the vicinity of the transducers was noticed and this continued in subsequent years with two to four animals seemingly unaffected by the device.
Geiger and Jeffries (1986) reported on the use of acoustic deterrents to carry out a 'drive' designed to flush harbour seals from Youngs River, Washington, using a technique previously tried by Mate and Miller (1983). Two boats motored slowly down the river while towing acoustic deterrents until they reached the mouth of the river where an 'acoustic barrier' (sound emitting devices arranged in a line across the river mouth) was switched on. Interviews with local fishers were used to assess the effect of the 'seal drive'. They reported a temporary reduction in seal interactions which quickly returned to maximum levels after just 2-3 days. Seals seemed to quickly learn strategies to avoid the barrier, with an account of at least one seal swimming near the sound source with its head out of the water. They concluded that AHDs were not completely successful, and after longer periods of use in attempts to deter seals from gill-nets, predation returned to previous levels or even higher when the device was active.
Westerberg et al. (1999) used a Lofitech device to protect salmon and whitefish trapnets in the Bothnian Gulf during 1997 and 1998. The ADD was activated on an intermittent schedule, and by comparing the proportion of catch that was damaged by seals during on and off periods, they showed that four of five trials experienced significantly lower predation rates while the device was active. Again, it is interesting to note that despite experiencing damage levels of up to 50% of the catch when the device was active, the subjective opinion of the fishermen was that the ADD had been effective at deterring grey seals. This highlights the fact that 'effectiveness' can be a relative metric, dependent upon expectations as well as economics.
Yurk and Trites (2000) tried to prevent harbour seal predation on out-migrating salmonid smolts, occurring under two bridges across the Puntledge river in Courtenay, BC. The (Airmar) ADD was found to be the most effective of the methods employed, significantly reducing the number of seals feeding. However, the trial was short at just 14 days and thus does not provide any information on long-term efficacy of acoustic deterrents.
A limited trial of acoustic deterrents to prevent fur seal bycatch and depredation in the New Zealand hoki fishery was reported by Stewardson and Cawthorn (2004 appendix 5.1a). Initial tests in 1990 used an ADD manufactured by a Swedish company 'Kemers Meskin AB', a highly directional device, apparently emitting between 200 and 210 dB re 1 µPa ( RMS or peak not stated) with peak frequency at 10 kHz. They stated that the system was tested in both near-shore and offshore waters as well as coastal locations close to haulout sites. Offshore results were reported as 'equivocal' with some fur seals moving rapidly away while others remained within 1-2m of the transducer for 15-20 minute periods. Analysis showed no significant avoidance behaviour. Near shore results were positive for small and medium sized animals, while larger animals initially showed indifference and later came toward the device. As discussed above, the same device had limited success at evoking an aversive response from juvenile fur seals at a haulout site.
An investigation by the North Eastern Sea Fisheries Committee ( NESFC), UK, showed some effect of a Lofitech device on the rate of depredation experienced by salmon and cod fishermen operating on the Yorkshire Coast ( NESFC, 2008). By recording the proportion of the catch which showed bite-marks, they found an average predation rate of 12.3% in 2006, which fell to 6.5% in 2007 after the introduction of four acoustic deterrents. A longer controlled study and more detailed analysis are needed to show that this effect was really due to the ADD. Perhaps more interesting is the feedback from the fishermen who used the devices, all of whom believed that the system had a positive impact on the quantity of undamaged fish that was landed.
Graham et al. (2009) installed Lofitech scarers in shallow sites in two Scottish salmon rivers, the North Esk and Conan, in an attempt to prevent seals from moving upstream. They estimated the number of seals in each river based on the number of coincident observations and the positions and timing of sightings. Although they were not able to carry out photo-identification, they claim that the absolute abundance of seals in the river did not change after the introduction of the ADD. They did show, however, that the number of seals upstream of the seal scarer was significantly reduced (by around 50%). It is not clear why such a difference should exist between this and other studies using the 'acoustic barrier' technique (Geiger and Jeffries, 1986), but possibilities include the very shallow water increasing the efficacy of the ADD and/or the motivation of the seals, which may have been lower at this site than elsewhere. Nevertheless, this study shows the difficulty in generalising from individual field trials.
The Lofitech device was also used by Harris (2011), who tested its effectiveness at reducing depredation of fixed, near shore salmon nets by grey and harbour seals in Scotland. Observations of seal interactions with the nets were made during 124 trial periods over two years (mean observation period 1.6 hours). The number of sightings was significantly reduced, as was the amount of time seals spent in the area. While the ADD was on, catch per unit effort also increased by approximately 33%. In the first year, 2009, no seals were seen within 80m of the device, but in 2010 there were 7 sightings within this area, potentially suggestive of habituation. 56% of seal sightings were photo-identified and this showed that 63% of encounters were with just two seals, indicating that only a small number of seals were using the site.
|KG No.||Knowledge Gap|
|39||What proportion of seals have naturally impaired hearing? How does this change with age?|
Scordino (2010) summarises the use of Pulsed Power Devices ( PPDs) in efforts to reduce pinniped predation on salmonids in North America. These devices rely on high amplitude acoustic signals creating an aversive response and it is therefore included as an acoustic device. First tested on pinnipeds in the early 1980s, these devices discharge high levels of electrical energy, creating ionised gas across the 'arc-gap'. A wave of compression then emanates from the PPD, followed by an acoustic wave calculated at 240 dB re 1 µPa (peak). The pulse duration was below 500 microseconds, and the energy released was 1.8 kJ. This type of device was tested on captive California sea lions by Finneran et al. (2003), who found temporary avoidance of the device, and no evidence of hearing damage (although the device tested here had a much lower output of <183 dB re 1 µPa RMS). Scordino (2010) notes, however, that these devices have yet to be tested in 'field conditions', and the size of the device, at 98kg and 2 metres in length, could make deployment impractical.
Overall, it is clear that pingers are effective in minimising bycatch of some small cetaceans. They appear to do this by displacing the target animals (Dawson et al., 2013). Pingers may also be effective in some cases in minimising whale entanglement, but this remains to be fully explored. They do not appear to be effective in reducing seal bycatch, and may indeed increase seal/net interactions by acting as a "dinner bell" when signal frequencies are within seal hearing ranges.
This effect can be contrasted with the much more powerful ADDs which have been shown to be effective to some degree at reducing pinniped depredation, for limited periods of time at least. The Lofitech device in particular has shown promising results in Scottish and Swedish capture fisheries. No studies have found complete cessation of depredation, and in some cases there may have been a small number of individual animals which were unaffected by the ADD ( e.g. Harris, 2011).
Several devices are being marketed to minimise cetacean depredation in longline fisheries, but studies on their efficacy are too limited to draw any conclusions. Less powerful pingers used in gillnet fisheries have yet to be proven as a means of minimising depredation by cetaceans in such fisheries, at least beyond the short term.
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