Aquaculture - use and efficacy of Acoustic Deterrent Devices (ADDs): report

2 Introduction

2.1 Depredation in aquaculture

Farming of Atlantic salmon (Salmo salar) in Scotland is an important and growing industry. Production has increased from less than 40,000 tonnes of production in 1990 to over 200,000 tonnes in 2019. Farmed salmon is currently the UK's largest food export product by value. It directly employs around 2,400 people, with a further 8-10,000 jobs in downstream processing and associated roles. It has particular economic importance in coastal and rural areas, where few employment opportunities exist. Furthermore, the Scottish Government has a stated ambition to increase salmon production, to double the economic contribution of the sector from £1.8 billion in 2016, to £3.6 billion by 2030, and to double the number of jobs to 18,000 by 2030 (Scottish Government, 2020a). As of December 2020, there were around 220 active finfish farm sites in Scotland (Scotland's Aquaculture, 2020).

The seas around Scotland are important for marine wildlife, supporting at least 22 species of marine mammals, including seven relatively common species of cetacean (bottlenose dolphin - Tursiops truncatus, harbour porpoise – Phocoena phocoena, minke whale – Balaenoptera acutorostrata, white-beaked dolphin – Lagenorhynchus albirostris, Risso's dolphin – Grampus griseus, common dolphin – Delphinus delphis and killer whale – Orcinus orca) as well as large numbers of two species of pinnipeds (grey and harbour seals - Halichoerus grypus and Phoca vitulina, respectively). Marine mammal populations around Scotland inevitably interact with finfish farms to some extent, and these interactions can be negative to both the wild animals and the aquaculture industry. The most significant and problematic of these interactions occur between finfish farms and seals. Scotland has a population of around 122,500 grey seals representing around 83% of the UK population, and a minimum population of 26,900 harbour seals representing around 82% of the UK population (SCOS, 2019).

Depredation by seals at finfish farms is a serious welfare and economic concern for the Scottish aquaculture industry, occurring at around 73% of finfish farms (Northridge et al., 2013). The precise mechanism of predatory attacks is not well understood, but seals are known to manipulate finfish farm nets in order to attack and kill fish from the outside (Coram et al., 2016). As well as injury and mortality of stocked fish, predators can cause stress to stocked fish (Barcellos et al., 2007), potentially reducing growth rate and tolerance to disease (although this has not been studied in the context of seal depredation). Seals can also cause damage to fish farm infrastructure. Damage by predators to nets has been reported as one of the largest causes of fish escapes in European aquaculture (Jackson et al., 2015).

A combination of lethal and non-lethal management and mitigation options have been used by managers to reduce the impact of predators in aquaculture. Until 2011, the lethal removal of seals to alleviate depredation was largely unlicensed. However, since the introduction of the seal licensing system in 2011 through the Marine (Scotland) Act 2010, there has been an overall reduction in the numbers of seals targeted and subsequently shot under license as a last resort (Scottish Government, 2020b). Throughout the period of licensed lethal removal, the aquaculture industry maintained an ambition to reduce the number of seals killed under licence for the protection of stocked fish to zero (RECC, 2018), Changes to the Marine (Scotland) Act 2010^[1] which came into force on 1 February 2021 mean that licences can no longer be granted authorising the taking or killing of seals for the purpose of preventing serious damage to fisheries or fish farms, or to protect the health and welfare of farmed fish. There is therefore a requirement to find additional options for reducing the occurrence of depredation caused by seals.

One of the most regularly used methods to address seal-aquaculture interactions is the use of Acoustic Deterrent Devices (ADDs), which has increased substantially on the west coast of Scotland from 2006 to 2016 (Findlay et al., 2018). These devices produce underwater sounds which aim to deter seals in order to reduce the risk of depredation or stress caused to fish by predatory behaviour. However, their use in aquaculture to deter seals may cause disturbance to cetaceans under certain conditions (Brandt et al., 2013; Johnston, 2002; Mikkelsen et al., 2017; Olesiuk et al., 2002). Furthermore, limited research has been undertaken on whether the use of ADDs reduces depredation, and there is currently little scientific evidence to support their long-term use. Conversely, several studies have reported habituation by seals to the most regularly used signal types (Götz & Janik, 2010; Ross, 1988; Sepulveda & Oliva, 2005), but the available evidence is very limited.

There is therefore a clear requirement for a better understanding of the extent and use of ADDs at Scottish finfish farms. In particular, it is important to improve understanding about how many devices are currently in use, their acoustic properties, how they are used, how effective they are in reducing depredation, and what impacts they may have on non-target species (e.g. cetaceans).

One of the aims of this project was to collate information from all available data sources, including information held by the aquaculture sector, to provide a description of the current extent of ADD use. In addition, data was also collected on the rate and level of depredation by seals. These data together, provide the best available evidence of ADD efficacy, as well as other anti-predator measures such as modern netting materials and weighting systems, at reducing depredation.

2.1.1 Anthropogenic conflicts with marine predators

Legal protections and the cessation of exploitation of marine mammal species in many parts of the world have contributed to increasing populations, particularly of pinnipeds (Chasco et al., 2017). Whilst this is generally viewed as a conservation success story, it may have led to an increase in negative interactions with some marine industries, such as fisheries and aquaculture in the context of increasing anthropogenic demand for wild-caught and farmed fish (Gales et al., 2003). In some cases, conflicts with wildlife conservation efforts have also emerged. For example, increased pressure from pinniped populations has been linked to reduced recovery of wild salmonid stocks (Butler et al., 2006; Yurk & Trites, 2000).

Fisheries and aquaculture suffer from loss of value as a result of direct depredation of fish (e.g. Figure 1), through damage to infrastructure such as netting and, in the case of wild capture fisheries, possibly through increased competition for resources (MMO, 2019). Seals were reported to be a source of depredation at around 73% of finfish farms, and Northridge et al., (2013) found that almost 1.4 million fish were reported lost to seals at 87 sites over a 129-month period, equating to a conservative estimate of around £26,000 per site per year of lost revenue. Figures produced by the Scottish Salmon Producers Organisation (SSPO) suggests that 500,000 fish were lost to seal depredation in 2020 alone^[2]. With farmed salmon prices of around £5 per kg, depredation of harvest weight fish costs the industry between £15 and £35 of revenue per fish. Damage to nets presents an additional cost, requiring maintenance by divers and risking the potential escape of large numbers of farmed fish, which presents a conservation concern for wild salmon stocks.

In the context of finfish aquaculture, conflicts with pinnipeds present an additional concern in terms of the welfare of farmed fish. Aquaculture practitioners have moral and legal obligations for the protection of their fish through the Animal Health and Welfare (Scotland) Act 2006 and must manage any wildlife interactions accordingly. As well as injury and mortality, pinniped attacks can cause stress to captive fish which is in itself a welfare concern. Stress to captive fish is linked to reduced growth rate and increased susceptibility to disease (Barcellos et al., 2007).

2.2 ADD usage

2.2.1 Past ADD use

Since their commercial development in the 1980s, ADDs have been used in attempts to deter many different species of marine mammals in a variety of applications, including: protecting migratory fish in river fisheries (Graham et al., 2009) or marine bottlenecks (Mate & Harvey, 1987), in mobile and static fisheries (Gosch et al., 2017; Königson, 2006; MMO, 2020; Petras, 2003; Westerberg et al., 1999) and as a mitigation tool in offshore renewable energy development (Thompson et al., 2020). Where the term ADD is used in this document, it is generally applied to all acoustic devices designed to deter seals, unless otherwise stated.

The use of ADDs in Scottish aquaculture has been increasing since it was first assessed in 1985, when four of 41 (9.7%) sites were using them as a mitigation tool (Hawkins, 1985). By 1988 this had risen to eight sites out of 45 (18%) (Ross, 1988); an increase that continued though the 1990s to 52% in 2002 (Quick et al., 2002), and a similar percentage (49%) was reported again in 2010 (Northridge et al., 2010). The use of ADDs has become more common on the Scottish west coast from 2006 to 2016 (Findlay et al., 2018), and interview surveys with aquaculture site managers suggested that Airmar, Terecos and Ace Aquatec equipment were most widely used in Scottish aquaculture in 2010 (Northridge et al., 2010). Results from acoustic surveys found similar results, with most ADD noise detected on the west coast between 2011-2015 attributed to 'Airmar-type' devices (>75%; Findlay et al., 2018).

2.2.2 Rationale for ADD use

Despite the widespread use of ADDs at finfish farms, there is limited published evidence to support the long-term effectiveness of ADDs (reviewed in Coram et al. (2014). To date, scientific research has largely focused on assessing the potential impacts of ADDs on non-target species, rather than on quantifying their efficacy in deterring predators. A comprehensive review of the current evidence for effects of different devices on different species is available from a Joint Nature Conservation Committee (JNCC) report (McGarry et al., 2020).

Effective deterrence is thought to rely on altering the relative costs and benefits to the individual predator by creating a perceived risk associated with human resources, and ADDs are hypothesised to do this by either inducing pain or distraction in the target animals (Schakner & Blumstein, 2013). Captive grey and harbour seals have been shown to find certain sound types aversive and appear not to habituate to these signals (Kastelein et al., 2017; Kastelein, Heul, et al., 2006). One study showed sensitisation toward sound signals that elicited a startle-response (Götz & Janik, 2011). However, some animals (two out of seven) were found not to respond to the startling signals.

Playback experiments at sea, outside the context of aquaculture, have found mixed behavioural responses to ADD sounds. A Lofitech ADD (not in use in Scottish aquaculture) reliably elicited a response from tagged harbour seals at ranges of less than 1 km, but responses did not always result in substantial movements away from the sound source (Gordon et al., 2019). A simulated ADD signal (based on the Lofitech with reduced source levels) caused an increase in observations of seals within 100 m of the ADD signal when it was switched on (Mikkelsen et al., 2017), suggesting that seals do not always find such signals aversive. Additionally, if seals learn to associate an ADD with a source of low cost resources, they may be drawn to the sound source – often termed the 'dinner bell effect' (Mate & Harvey, 1987).

While it may seem sensible to draw parallels from other applications, it is important to remember that the behavioural context at a finfish farm may be very different from other situations where research into ADD has been conducted. It is not possible to accurately replicate in captivity the behavioural context where depredation occurs (i.e. motivation and hunger). Trials conducted at sea but away from finfish farms will also have a different behavioural context and may therefore elicit a very different suite of behavioural responses (Coram et al., 2014). Likewise, trials conducted with one ADD type may not be suitable evidence for inferences relating to other ADD types.

Only a small number of 'real-world' studies have been conducted into the efficacy of ADDs. In addition to the studies reviewed by Coram et al. (2014) we are aware of three additional studies of ADD use in aquaculture. The use of the acoustic startle reflex to deter pinnipeds has shown success in early trials of a GenusWave device. Götz & Janik (2015) reported a significant reduction in the number of seal tracks within 250 m of the device, and seal distribution was not affected at distances further away from the farm, suggesting a very localised deterrent effect. A longer-term trial at Scottish finfish farm showed a significant reduction in depredation over a period of 12.5 months (Götz & Janik, 2016). Trials have so far been limited in scope, and evidence from commercial application of this device is required before broad conclusions can be made about efficacy. In another study, use of Ace Aquatec US3 and Airmar dB Plus II equipment was found to reduce depredation at Scottish finfish farms by 70% and 50% respectively, compared to baseline with no ADD use, while the use of a Terecos ADD apparently had no effect (Whyte, 2015).

2.3 Policy background

There has been a long-held ambition by the aquaculture sector to reduce the number of seals shot to protect Scottish aquaculture to zero (RECC, 2018).

Legislation passed in the Scottish Parliament in June 2020 (The Animals and Wildlife (Penalties, Protections and Powers) (Scotland) Act 2020)) removed two provisions by which licences could be granted authorising the taking or killing of seals for the purpose of protecting the health and welfare of farmed fish, and to prevent serious damage to fisheries or fish farms. As a result of these changes, which came into force on 1 February 2021, there is consequently a need for effective additional management methods to be developed and implemented. The use of acoustic deterrents is seen by the industry as one effective method.

The Animals and Wildlife (Penalties, Protections and Powers) (Scotland) Act 2020 also includes a requirement for Scottish Ministers to provide a report to the Scottish Parliament on the use of ADDs, including; "information on the use made of acoustic deterrent devices on Scottish fish farms, any known impacts that the use of acoustic deterrent devices has on marine mammals, and consideration of whether the use of acoustic deterrent devices on Scottish fish farms is sufficiently monitored".

The Conservation (Natural Habitats, & c.) Regulations 1994 (as amended) ('Habitat Regulations) which apply in Scotland, include protection for cetaceans which are European Protected Species (EPS). Under regulation 39 (1) and (2), it is an offence to deliberately or recklessly capture, injure, kill or harass a wild animal of EPS, and deliberately or recklessly disturb any cetacean. Where an activity takes place that could constitute an offence, a European Protected Species licence (EPS licence) will be required. Revised guidance in relation to the protection of marine EPS from injury and disturbance in Scottish inshore waters was published in 2020 (Marine Scotland, 2020c), along with an information note to clarify the circumstances in which an EPS licence to use an ADD would be required (Marine Scotland, 2020b). Licences may only be granted if there is a licensable purpose, there are no satisfactory alternatives, and the actions will not be detrimental to the maintenance of the population of the species concerned at favourable conservation status. Licensable purposes include prevention of serious damage to livestock or fisheries.

In addition to their status as EPS, several species of cetacean are also protected by a network of marine protected sites comprising marine protected areas (MPAs) and European sites (Special Areas of Conservation, SACs). The introduction of the Inner Hebrides and the Minches SAC for harbour porpoise focused attention on ADDs as a potential significant source of underwater noise pollution, and a potential source of widespread disturbance in that area. The designation of the SAC created a requirement to ensure that harbour porpoise populations are not impacted within the site. New applications for fish farms within the Inner Hebrides and the Minches SAC are required to provide information on predator management measures adopted, including information relating to the use of ADDs. Such information may not be held for sites which pre-date the SAC designation and have not required any subsequent amendments to planning permission. Further, MPAs recently designated for the protection of Risso's dolphins (North-East Lewis) and for minke whales (Sea of the Hebrides) have conservation objectives that require the maintenance of the protected features in favourable condition. There is a duty on regulators to ensure there is no risk of hindering the achievement of the conservation objectives of the MPA before consenting an activity such as ADD use associated with a new fish farm application.

The Scottish Government is committed to the UK Marine Strategy (DEFRA, 2019), which requires healthy populations of birds and marine mammals as part of 'Good Environmental Status' (GES). An essential step in achieving GES is the establishment of adequate monitoring programs (Dekeling et al., 2016), and ADDs are listed by OSPAR Monitoring Guidance for Underwater Noise in European Seas as an important sound source to be monitored. In response to this requirement, in the UK information is routinely recorded for some types of underwater sound sources through the Marine Noise Registry (MNR), administered by the Joint Nature Conservation Committee, and includes some information on the use of ADDs when used for offshore mitigation (JNCC, 2020).