Evaluating and Assessing the Relative Effectiveness of Acoustic Deterrent Devices and other Non-Lethal Measures on Marine Mammals

Marine Scotland commissioned a research project aimed at gathering literature and data into the effectiveness of non-lethal measures of deterring marine mammals from a range of activities (e.g. fish farms, renewable developments etc.). This review attempt

8 Knowledge Gaps and Research Recommendations

8.1 Knowledge Gaps

Here we have used the term "knowledge gap" to refer to any topic arising within the report where uncertainties exist in the scientific understanding. Knowledge gaps have been highlighted throughout this text at appropriate points with the intention of clarifying the limitations of current understanding in each area. Table 6 collates these points, and reveals that a large amount of uncertainty exists in some of the areas addressed in this report. Where appropriate, these points have been expanded into recommendations for research below ( section 8.2).

Table 6 Knowledge gaps as listed in the body of this report

Section KG No. Knowledge Gap
2.1.1 1 The extent and monetary cost of seal depredation at Scottish fish farms is unknown. 2 What effect do different netting materials have upon seal depredation of salmon? 3 Exactly what has been - and what should be - classified as seal predation mortality? 4 How are salmon growth rates affected by seal presence and depredation? 5 Is there a relationship between seals depredation and disease among farmed salmon? 6 Quantification of welfare concerns - to what extent do seals injure without killing fish?
2.1.3 7 What specific mechanisms do pinnipeds use to damage fish within nets?
2.2.1 8 Exact acoustic output of all devices and an appropriate metric (or suite of metrics) for comparison of different signal types.
2.2.1 9 Effect of fouling and voltage drop on signal output (under full range of operating conditions). 10 What is the relative efficacy of different ADD deployment 'strategies', and how can they be appropriately compared? 11 How many sites have been denied approval for ADD use under planning regulations, and what criteria have been used to assess applications? 12 Total extent and distribution of ADD usage in Scotland is currently unknown. 13 Over what maximum range are cetaceans likely to be impacted by ADDs? 14 How can the effectiveness of ADDs be measured and compared, and what level of effectiveness is tolerable? 15 The effectiveness of ADDs in reducing seal depredation to stocked fish remains unclear. An experimental approach to address this fundamental uncertainty is difficult for economic and fish welfare reasons. 16 Effect of motivational state and context in mediating and modifying aversive response to ADDs.
2.3.1 17 How does stocking density influence seal behaviour and depredation rate?
2.3.1 18 Salmon behaviour within nets and in response to depredation is poorly documented, particularly at night.
2.3.1 19 How does net tensioning affect the ability of seals to remove fish?
2.3.1 20 How important are dead fish (morts), and their removal or concealment in motivating or preventing seal depredation?
2.3.1 21 How are anti-predator nets utilised internationally to avoid common problems experienced in Scotland?
2.3.2 22 The "rogue seal" hypothesis, and the rate at which removed seals are replaced is currently unclear.
2.3.2 23 How can recovery of seal carcasses be improved?
2.3.2 24 How can information about the demographic parameters of seals shot be improved?
2.3.2 25 It is unclear to what extent lethal removal is effective in minimising damage. No studies have looked at how depredation rate is affected by lethal removal. 26 Which emetics are most effective and what are the minimum doses required for CTA? 27 Are there any harmful physiological effects on seals treated with CTA, and if so, how can they be minimised. Is CTA sufficiently specific to salmon to leave the seals' normal diet of wild fish unaffected? 28 Are there any environmental effects of CTA? 29 How can baits for CTA best be prepared and presented to wild seals at salmon farms? 30 What patterns of "treatment" are most effective? Should baits be presented routinely or only when problems become evident? 31 Are there seasonal difference in when and how CTA should be use? Should there be "closed seasons"?
2.3.4 32 Behavioural aspects of electrical deterrence: how will behaviour be modified by context and motivation?
2.3.4 33 Practical aspects of electrical deterrence: engineering solutions are lacking and will be required before deployment in real-world applications can be feasible.
2.3.5 34 What legal and ethical restrictions would affect the use of trapping for translocation, conditioning or lethal removal?
2.3.5 35 What would the monetary cost of implementing such a trapping system be?
3.2 36 Efficacy of devices designed to deter depredating odontocetes in capture fisheries is currently unknown.
3.2 37 Efficacy of low frequency devices for deterring baleen whales is unknown.
3.2 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 39 What proportion of seals have naturally impaired hearing? How does this change with age?
4.2 40 Empirical measures of displacement movement rates are required in order to improve the TTS risk modelling approach. Appropriate movement models are the limiting factor in predicting risk of TTS.
4.3 41 It is unclear whether auditory preference/aversion is transferable between species.
4.3 42 Effects of absorption and reverberation on different signal types have not been shown, and could be prohibitive to long-range effectiveness of complex signals. 43 To what extent can a learnt response to a specific signal ( e.g. non-response to aquaculture ADDs) be transferred to a different context?
5.2 44 The acoustic output of tidal energy devices in all states of operation is unknown.
5.3 45 At what range will tidal turbines be detectable above ambient/background noise?
5.3 46 To what extent can noise hotspots in tidal areas be predicted based on parameters such as benthic composition? How stable are they spatially and temporally?
5.3 47 A greater understanding of the response elicited by existing deterrent devices, how this varies between species and contexts, and how this is likely to change over time.
5.3 48 A greater understanding of how marine mammals currently utilise tidal environments, and how this is likely to be affected by new structures and activities and additional sound sources.
6 49 Signal types which can reliably elicit a predictable and useful response in reducing risk of ship-strikes are currently unavailable.
7.2.3 50 Reliable audiogram data (or equal loudness contours) are not available for several of the species found in Scottish waters ( e.g. minke whale, white-beaked [ Lagenorhynchus albirostris] and Atlantic white-sided [ Lagenorhynchus acutus] dolphins). 51 Equal energy hypothesis for TTS does not seem to hold in all circumstances. A universal relationship between signal duration, intensity and hearing impact has not yet been described.
7.2.7 52 Realistic movement models for animals (particularly porpoises and seals) in the vicinity of ADDs.
7.2.7 53 Hearing damage caused by ADDs on wild populations of seals in particular seems possible, but has not yet been proven.
7.3.1 54 Is the Terecos device consistently less aversive to harbour porpoises than other ADDs?
7.3.4 55 Responses of baleen whales (and several other less studied species) to ADDs in Scotland are not clear at present.
7.4 56 Likely total extent of exclusion and disturbance of ADDs on different species.
7.4 57 Population level significance of potential exclusion of cetaceans by ADDs.
7.4 58 Population level significance of potential disturbance of cetaceans by ADDs.

8.2 Research Recommendations

The knowledge gaps identified in this review are summarised in Table 6. Below we outline a series of themed research recommendations to address these knowledge gaps and provide information necessary for a clearer understanding of the effectiveness of non-lethal measures. Each recommendation ('R') is accompanied by a suggested approach.

8.2.1 Aquaculture and Seals Baseline Data

Recent work highlights that data collected by salmon farms, in general, does not collect all of the pertinent information, is insufficiently detailed and is often difficult to access for research. A priority should therefore be given to the collection of more appropriate data on seal-fish farm interactions by the industry ( R1).

Research approaches: Work is required to define the data sources that could reasonably be collected to address key research questions. Key points to address include: what data are currently available to answer management questions (this would include assessment of reliable indicators of seal damage on fish), appropriate format for data collection, recommendations as to how data can be reliably collected (for example, can data fields be added to existing reporting requirements e.g. seal management reports, SEPA reporting), what mechanisms are required to ensure delivery of any additional data required. This is likely to require a close collaboration of researchers, industry practitioners and regulators. Information on the Efficacy of Existing Management

Reliable information is lacking on the effectiveness of management measures currently being employed. This is particularly important for those activities which have unintended negative consequences. Useful progress should be made by analysis of data from an improved reporting scheme (R1) but directed research into the effects of site specific management regimes should also be undertaken ( R2).

Research approaches: Where sufficient data exist, the efficacy of various existing management measures should be assessed by comparing predation rates at matched sites applying different management techniques. Key points to compare would include: net size and shape, net tensioning systems, locality of seal haulouts, stocking density, net cleaning regime, tidal flow rate etc. Experience has underlined that this will be an effective strategy only if industry partners are engaged and have a responsibility for delivering results.

Another potentially useful source of information is the large database of telemetry tracks which SMRU holds. These should be examined for instances where tagged seals seem to be spending time in the vicinity of fish farms and these could be compared with existing datasets on depredation. Lethal Removal

Depredation events sometimes lead to the removal of individual seals by shooting. There is a very poor understanding of this method and whether and how it is effective. Knowledge gaps include the types of seals (for example, species, gender and age of animals) removed, their recent diet, how reliably marksmen identify and remove "problem seals", how successfully and for how long does lethal removal provide relief from depredation. The success or otherwise of lethal removal needs further investigation ( R3).

Research approaches: Implementation of a strict recording structure including: on-site observation prior to lethal removal, photo-identification of individual seals and carcass recovery to determine whether removed animals match photo- ID "culprits", demographic characteristics (age, gender, health) of removed animals, stomach contents analysis (otoliths and DNA). Efficacy of ADDs

There is a need for information on the extent to which ADDs of different makes and design provide relief from seal depredation and/or reduce the number of seals that the industry requires to remove lethally ( R4).

Research approaches: Collection of improved data from salmon farms (above) may provide some insights. Information from sites where ADDs are not permitted to be used may be especially useful. Investigation of instances where ADDs cease to be effective, e.g. acoustic mapping of sound fields for comparison with effective ADDs.

A series of field trials could be conducted to address these issues. For example farms could be allocated existing ADD types according to a randomised controlled trial design once seal attacks start. This would allow unbiased comparisons to be made between the performance of currently available ADDs without leaving any farms "unprotected". The experimental design might allow site managers to opt to switch to an alternative device (also allocated randomly) if the first device was shown to be ineffective. This would allow development of a formal index of relative effectiveness of different devices, but could only be achieved with commitment of industry. Anti-Predator Nets

This project has highlighted that while anti-predator nets are rarely deployed in Scotland, they are routinely used in other salmon-producing countries. The reasons for this difference are not clear and should be investigated ( R5).

Research approaches: Dialogue with salmon producers and researchers working with anti-predator nets (and related techniques) in other countries, for example, in Canada, Chile and Australia into the effectiveness of these nets. A critical comparison of anti-predator net structure used abroad with those (previously) used in Scotland, followed by controlled trials of any promising modifications or new devices at one or more appropriate sites in Scotland.

8.2.2 Unintended Environmental Consequences of ADD Use Hearing Damage

The risk that individual animals may suffer hearing damage through exposure to ADDs is currently poorly understood. A potential risk has been identified through this review and it is most likely to affect seals that are motivated to remain close to fish farms with operating ADDs. Risk of hearing damage needs investigation ( R6).

Research approaches: Risk of hearing damage could be assessed by combining maps of sound fields with photo-identification and range measurement data (movement patterns) for seals at fish farms and using these data to calculate cumulative sound exposure. Another potential approach would be to catch seals at farms and use telemetry devices, including acoustic dose meters, to measure movements and exposure simultaneously. Existing telemetry datasets held by SMRU could also be examined to approximate acoustic exposure. The hearing sensitivity of captured seals that have apparently "habituated" or become resistant to ADDs could also be assessed. The inner ears of seals shot at fish-farm sites could also be examined for evidence of hearing damage. Any assessments of hearing sensitivities and potential damage would need to be made in the context of an understanding of these parameters in the wider population. Disturbance of Non-Target Species

Questions still remain about the extent of habitat exclusion and disturbance of non-target wildlife ( e.g. cetaceans) from ADDs. At least four different ADDs are being used in Scottish waters. These are likely to differ substantially in their potential effects on wildlife but effects of only one type have been measured. Impacts of other devices on non-target species should be investigated ( R7).

Research approaches: In Scotland, harbour porpoises can be used as a representative species because they are locally abundant. Well proven, effective passive acoustic monitoring methods exist to quantify their displacement due to ADDs. Research using a balanced experimental design can be used to quantify and compare the degree of habitat exclusion caused by the ADDs most commonly used in Scottish waters. This type of monitoring approach has been applied successfully several times at Scottish salmon farm sites so there is little technical risk. As with most research, close cooperation from the salmon farms involved will be essential. This work could provide a disturbance index for each ADD type which, in conjunction with data on the effectiveness of devices in reduction of seal depredations, could be used by regulators to make recommendations. Ecological consequences of habitat exclusion

The first step towards understanding the population consequences of habitat exclusion caused by ADDs is to measure small cetacean densities in the regions around fish farm sites and at nearby control sites. For porpoises this can be done most efficiently using a combination of visual, towed hydrophone and static acoustic monitoring. Further work is needed to investigate the ecological consequences of habitat restrictions on small cetaceans ( R8)

Research approaches: Quantification of porpoise densities year round in the wider vicinity of several representative farm sites including at times when ADDs are not being used. A combination of visual and towed acoustic surveys in conjunction with static monitoring at appropriate locations is likely to be most effective technique. These data, in conjunction with measures of disturbance, could be used to advise on appropriate ADD types for particular sites.

8.2.3 Development of New Management Approaches

If a combination of improved management and containment practices (including ADDs) are not able to reduce seal depredation to the point where levels of lethal removals are considered acceptable by regulators then new management options clearly need to be explored ( R9). Two examples are given: Electric field deterrents

Research supported by SARF is ongoing at SMRU. Where necessary, this should be extended and continued. Conditioned taste aversion

This review has identified CTA as a particular area where research is warranted. Both captive and field studies are required as outlined in section

8.2.4 Alternative Applications Using Sound for Management Active Acoustic Mitigation of Risk from Pile Driving and Explosions

Given Scotland's ambitious plans for development of offshore wind farms and the ongoing removal of abandoned well heads and other offshore oil infrastructure the development of effective and affordable means for mitigating the risks of hearing damage from pile driving and explosives is urgently required.

A method that shows considerable promise is the use of aversive sounds to move animals out of areas where they would be at risk using aversive acoustic signals. Research is needed to show how animals move in response to different sound types and how such signals could be used to provide practical and predictable mitigation ( R10). Potential research approaches for Scottish priority species are outlined below.

Research approaches. Different research approaches will be needed for different marine mammal groups:

  • Seals

Recent work funded by Scottish Government has developed and demonstrated an approach combining a new detailed telemetry system with low-cost, at-sea playback, which can be used to provide the detailed information on animal movements in response to acoustic signals that is needed to develop aversive sound mitigation techniques for seals. This approach should be applied to both harbour and grey seals and conducted either within areas where mitigation techniques are required or within habitats that closely match those areas.

  • Harbour porpoises

An approach combining the use of static acoustic monitoring devices with detailed observation of behavioural responses to controlled exposures has been shown to be effective with this species. Trials may need to be completed with a greater range of candidate acoustic signals. The development of live capture methods to enable telemetry would greatly assist such work.

  • Minke whales

Controlled exposure of animals would be likely to be successful but methodological and equipment development ( e.g. suction cup telemetry devices) may be required as precursor.


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