The cetacean bycatch problem – urgent action is required
It is estimated that 600,000 marine mammals are bycaught in fisheries each year and that fishing poses the single greatest threat to the survival of many marine mammal populations globally. It is expected that 98% of these deaths are attributed to set nets (Read et al. 2006). The prospects for many small, coastal cetaceans remain bleak, particularly for those populations in developing countries with large small-scale fishing fleets, where fisheries bycatch is the primary pressure. To date, management responses to these rapid declines in cetacean populations have been rather late and at a stage where recovery opportunity is diminished e.g. Franciscana, Maui, Vaquita, Baja, Yangstze and Baltic harbour porpoise. Given the imminent, dire population projections for many coastal cetaceans, management approaches need to be proactive rather than reactive, if they are to be saved.
Top-down management measures such as reduced fishing effort, gear switching, spatial or temporal closures are arguably optimal solutions to cetacean bycatch, issues, realistically they are often slow to implement, and are met with resistance and non-compliance by fishers in the absence of rigid monitoring or enforcement programmes.
Effective technical measures that promote gear selectivity without fundamentally changing the fishing operation are likely be adopted more favourably by fishers and thus start achieving conservation outcomes more rapidly. Technical measures that are readily available, pragmatic, affordable and proven to mitigate bycatch in set net fisheries are currently limited and pingers offer a tried and proven solution (Hamilton & Baker 2019).
Common misconceptions about pingers
That said, a number of common misconceptions have arisen about the use of pingers as bycatch mitigation tools over the decades. As leaders in the field of acoustic deterrents we decided to address the key potential issues directly, to understand whether they are founded in reliable evidence, and if so, whether we can do anything to resolve them. We used the latest research findings and, where necessary, conducted our own experiments.
Some authors suggest that pingers may not be successful bycatch mitigation devices for all cetacean and pinniped species (Dawson et al. 2013, Hamilton & Baker 2019).
For example, they have been described as acting as ‘dinner bells’ for California sea lions (Zalophus californianus), South American sea lion (Otaria flavescens) and common bottlenose dolphins (Tursiops truncatus), with individuals of these species having been observed depredating nets equipped with pingers (e.g. Bordino et al. 2002, Read et al. 2003, Carretta & Barlow 2011, Snape et al. 2018).
That said, early studies that reported pinniped depredation all deployed low frequency (10kHz) pingers – presumably as this was the frequency mandated for use in US fisheries and the acoustic consensus for pinger use at that time. The audiograms for California sea lion and other pinnipeds show optimal hearing at 3-20kHz (Mulsow 2012, Erbe et al. 2015), meaning easy detection of low frequency pingers attached to nets and the subsequent “dinner bell” association.
However, pingers are changing and recent trials with higher frequency “seal safe” pingers (50-120kHz) that are tailored to transmit outside the optimal hearing thresholds of pinnipeds eliminated the dinner bell effect noted earlier by Bordino et al. 2002 when low frequency pingers were dismissed as a mitigation measure for preventing bycatch of the Vulnerable Franciscana dolphin (Pontoporia blainvillei) in coastal set net fisheries off Brazil (Lopez et al. in press).
Furthermore, recent trials in Norway using 10kHz pingers found that the bycatch of harbour seal (Phoca vitulina) in set net fisheries there was three times higher than using no pingers or nets equipped with 50-120kHz pingers (Øien & Haug 2017). If the pings can no longer be detected by seals and the catch remains safe in the nets, this excuse for not using pingers is no longer valid.
There has been concern that the initial aversive reaction of cetaceans to the sound of pingers may wear off over time, leading to a reduction in their effectiveness – commonly referred to as habituation (e.g. Cox et al. 2004, Cox et al. 2001 , Amano et al. 2017). Whilst these concerns are often cited by managers as a reason to prevent pinger uptake, the evidence base from the two longest pinger trials globally don’t show any evidence of habitation (Koschinski and Culik 1997, Palka et al. 2008, Carretta and Barlow 2011).
Research using our Banana Pingers supports these findings; Swedish (2017) and UK (2013) trials both experienced 99.8% reduction in rates of cetaceans around nets equipped with our Banana Pingers and zero habituation over prolonged periods of time. The figure below shows acoustic evidence from the Swedish Baltic that the detectable clicks per minute (DPM) of cetacean species remained consistently low in the presence of the Fishtek Banana Pinger throughout the study period demonstrating empirically that habituation wasn’t occurring. These results support the long-term observations from fisheries mandated to use pingers.
In 2019 our own primary research with harbour porpoise in the UK found that the effect of the pinger was consistent across the period of study at all sites, and concluded that there was no habituation that would lead either to harbour porpoise ignoring the pinger and becoming more prevalent, or being significantly deterred by the pinger and avoiding the area longer term.
One difficulty with potential habituation is that there are two different fishery/cetacean interactions, and they are often conflated. Habituation to pingers by cetaceans who depredate (take fish out of fishermen’s nets) has been documented more often than when pingers are used to prevent incidental entanglement of passing cetaceans in fishing nets (Dawson et al. 2013). This is because cetaceans who are depredating nets benefit from an easy meal at the end of the interaction, they have an incentive to override their instinctive aversive reactions. The findings of all studies where accidental dolphin or porpoise entanglement is the issue show that pingers remain extremely effective bycatch mitigation.
A well-publicised paper by Palka et al. (2008) researched whether bycatch reduction using pingers was as effective in a commercial fishing setting as it appeared to be in scientifically controlled trials. It found “that pingers appear to have reduced the bycatch rate, particularly when the required number of pingers were used and in nets using mesh sizes of 15cm or less”.
However, some fisheries managers around the world seem to be mis-citing the paper, believing that it states that incorrect use by fishermen (e.g. trying to reduce costs by increasing the spacing between pingers, or inadvertently increasing spacing by not maintaining and confirming functionality of each pinger) made bycatch worse than not using pingers at all. This interpretation of the findings is causing management concern over pinger use around the world. In the UK, this management uncertainty has directly resulted in a lack of conservation action and continued bycatch in high risk fisheries.
Fishtek Marine spoke to Dr Palka directly about her findings, how they are portrayed in the paper, and how they are interpreted. She agreed that for many of the years of the study period, the analysis was undertaken without accounting for pinger failure rates, which is an important variable which should be considered. Although this limitation is explicitly stated in the discussion section, overwhelmingly (and disappointingly) the impression readers are left with is that incorrect use of pingers triples bycatch.
Looking at the data it is clear that when pinger functionality was high (see 2006 data from figure below) bycatch in hauls with an incomplete set of pingers was actually three times less than hauls without pingers, but as expected, not as effective as hauls where full pinger compliance was observed. Palka et al. (2008) only looks at 2006 data where pinger functionality is high, but we believe that if other years where high pinger functionality was confirmed were looked at, the same observation would be observed – that is, incomplete pinger use is better than no pingers but not as good as full compliance (see figure below) which is opposite to the take home message of the paper.
This is a concern that by using pingers, fishermen are adding noise to the marine environment which could exclude cetaceans from areas of sea. The worry is that widespread deployment of pingers could prevent animals being able to access their important supporting habitats.
There is no evidence to substantiate these predictions. In 2000 Larsen and Hansen looked at potential ensonification in the Danish gillnet fishery and estimated that, even if all Danish gillnets were equipped with pingers, less than 1% of the North Sea would be affected. They also noted that the use of pingers in a Danish trial had not prevented porpoises from getting entangled either in nets set without pingers nearby, or in nets set soon afterwards, suggesting a relatively limited (temporal and spatial) degree of exclusion.
Northridge et al. (2011) had similar results when they modelled different pingers, spacing, and fishing sectors and found that, even when fishing activity is at its most intensive, only between 0.04% and 11% of the total area of the Celtic Sea and Western Channel (SW England) could potentially be denied to cetaceans.
From our own research with Banana Pingers and harbour porpoise we have found that when pingers are active, harbour porpoise still remain detectable and are therefore not deterred from the fishing grounds. Empirical evidence is consistent with the anecdotal evidence from multiple fishers using pingers who state that deterrence is localised and temporary. Fishermen report that the harbour porpoise appear to stay back from the point source of the pinger. The deterrent effect is less pronounced with distance from the sound source and has no lasting effect as the harbour porpoise immediately return to the area when the nets are removed.
Although the results of trials and feedback from fishermen show that ensonification is not a problem for some species, it would not be correct to assume that it couldn’t occur for other species with different reactions to pingers and different ranges, especially if nets were set intensively in their important habitats. Carlström et al. 2002 concluded that a displacement effect by pingers is likely to be more prominent in coastal waters where access to bodies of water is limited and the consequence may be serious if the area is critical to the survival of the porpoise population.
Managers key considerations…
Acoustic Deterrent Device (ADD or ‘pinger’) studies and trials have now been conducted around the world for decades. Over the years they have produced varying results due to survey design, cetacean species, fishing gear type, inconsistent reliability of the pinger devices used in trials, and (mis)interpretation of findings by managers. Persistent myths about potential unintended consequences of pinger use are perpetuated by the regular citing of papers based on early studies. The perceived problems with pingers include concerns about impacts on other species, issues of habituation, incorrect use leading to increased bycatch rates, operational effectiveness and ensonification (Franse 2005).
However, since the early studies, pingers have developed considerably with vast improvements in their reliability and acoustics. Managers’ experiences of implementing pinger use as a bycatch reduction tool have also been documented. Importantly, the variability reported on the overall efficacy of pingers to reduce cetacean bycatch can often overlook the animal’s relationship with the fishery and consequently the uncertainty in the evidence base can be conflated without delineating whether the animals are targeting the nets as a food resource (depredating) or becoming unintentionally entangled by not detecting the net.
Where cetaceans depredate fisheries, the evidence underpinning the efficacy of pingers at reducing fisher-cetacean interactions is indeed unclear (Dawson et al. 2013). Conversely, in fisheries where cetaceans are not actively depredating, the evidence base for pinger use to mitigate bycatch effectively (including Delphinidae) is much clearer, and not limited to harbour porpoise. For example, a long-term study of pinger use in the Californian-Oregon drift net fishery showed a sustained, 50% reduction in short-beaked common dolphin (Delphinus delphis) bycatch over a 13-year period (Carretta & Barlow 2011). In Peru, accidental bycatch of common dolphin & dusky dolphins (Lagenorhynchus obscurus) was reduced by 37% when using pingers over a ten-year period (Mangel et al. 2013).
So when should pinger use be considered?
We believe the first question managers need to consider is the relationship between the cetacean and the fishery. If the cetacean are depredating (stealing fish) from the fishery then acoustic deterrents are much less likely to be long term tools to prevent cetacean-fisher interactions as the “dinner bell” effect is much more likely to manifest.
In all other circumstances, where the cetacean-fisher interaction is accidental, we would strongly advise pinger use.
Pinger use in fisheries that accidentally bycatch cetacea that are easily startled, such as harbour porpoise and other Narrow Band High Frequency (NBHF) communicators like Burmeister, hectors, Franciscana are likely to be highly effective at preventing fisher-cetacean interactions. This is because Narrow Band High Frequency communicators A full list see full list of NBHF communicators can be downloaded here.
Narrow Band High Frequency cetacean species likely to respond particularly well to pingers
Amano et al. 2017. Long-term effectiveness of pingers on a small population of finless porpoises in Japan. Endangered Species Research. Vol. 32: 35– 40, 2017
Bordino et al. 2002. Reducing incidental mortality of Franciscana dolphin Pontoporia Blainvillei with acoustic warning devices attached to fishing nets. Marine Mammal Science, 18(4):833-842 (October 2002)
Carlström et al. 2002. A field experiment using acoustic alarms (pingers) to reduce harbour porpoise by-catch in bottom-set gillnets. ICES Journal of Marine Science, Volume 59, Issue 4, 2002, Pages 816–824
Carretta & Barlow 2011. Long-Term Effectiveness, Failure Rates, and “Dinner Bell” Properties of Acoustic Pingers in a Gillnet Fishery. Marine Technology Society Journal 45(5):7-19
Cornwall Wildlife Trust 2013. The Banana Pinger Trial: Investigation into the Fishtek Banana Pinger to reduce cetacean bycatch in an inshore set net fishery. October 2013. A report by Abby Crosby, Nick Tregenza and Ruth Williams.
Cox et al. 2001. Will Harbour porpoises (Phocoena phocoena) habituate to pingers? Journal of Cetacean Research and Management 3(1)
Cox et al. 2004. Behavioral Responses of Bottlenose Dolphins Tursiops truncatus to Gillnets and Acoustic Alarms. Biological Conservation 115(2):203-212
Dawson et al. 2013. To ping or not to ping: the use of active acoustic devices in mitigating interactions between small cetaceans and gillnet fisheries. Endangered Species Research. Vol. 19: 201–221, 2013.
Franse 2005. Effectiveness of acoustic deterrent devices (pingers). Universiteit Leiden Centrum voor Milieuwetenschappen Leiden Juli 2005, 33 p.
Hamilton & Baker 2019. Technical mitigation to reduce marine mammal bycatch and entanglement in commercial fishing gear: lessons learnt and future directions. Rev Fish Biol Fisheries 29:223–247. doi: 10.1007/s11160-019-09550-6
Koschinski & Culik 1997. Deterring harbor porpoises (Phocoena phocoena) from gillnets: observed reactions to passive reflectors and pingers. Rep Int Whaling Comm 47:659–668
Larsen & Hansen 2000. On the potential effects of widespread pinger use for the Danish North Sea gillnet fishery. IWC paper SC/52/SM27.
NOAA, RIN 0648–AM05 Taking of Marine Mammals Incidental to Commercial Fishing Operations; Pacific Offshore Cetacean Take Reduction Plan Regulations in Federal Register / Vol. 64, No. 14 / Friday, January 22, 1999 /Rules and Regulations. National Oceanic and Atmospheric Administration 50 CFR Part 229 [Docket No. 990104001–9001–01; I.D. 111398D].
Northridge et al. 2011. Bycatch of Vulnerable Species: Understanding the Process and Mitigating the Impacts. Final Report to Defra Marine and Fisheries Science Unit, Project no MF1003. University of St Andrews. Defra, London, 99pp.
Øien & Haug 2017. Norway progress report on Marine Mammals 2017. NAMMCO/26/NPR-N-17
Palka et al. 2008, Effect of pingers on harbour porpoise (Phocoena phocoena) bycatch in the US Northeast gillnet fishery. Journal of Cetacean Research Management 10(3):217–226
Read et al. 2006. Bycatch of Marine Mammals in U.S. and Global Fisheries in Conservation Biology Volume 20, No. 1, 163–169 C 2006 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2006.00338.x
Snape et al. 2018. Conflict between Dolphins and a Data-Scarce Fishery of the European Union in Human Ecology 46(3)
Swedish Banana Pinger Trial Results (2017)