FUTURE BRIEF:Underwater Noise

June 2013Issue 7Revised version*

Environment

Science for Environment Policy

*This version of the report, published on 30 October 2013, replaces the earlier versions published on 28 June 2013 and 2 September 2013.

The contents and views included in Science for Environment Policy are based on independent research and do not necessarily reflect the position of the European Commission.

This Future Brief is written and edited by the Science Communication Unit, University of the West of England (UWE), BristolEmail: sfep.editorial@uwe.ac.uk

To cite this publication:Science Communication Unit, University of the West of England, Bristol (2012). Science for Environment Policy Future Brief: Underwater Noise. Report produced for the European Commission DG Environment, June 2013. Available at: http://ec.europa.eu/science-environment-policy

Introduction Types and sources of underwater noiseImpacts of underwater noise on marine lifeThe ultimate effects of underwater noise on people and societyMonitoring underwater noiseReducing the impact of underwater noiseKnowledge gapsSummary

Contents

Science for Environment PolicyUnderwater Noise

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ImagesPage 3: ©istockphoto.com/ultramarinfoto. Page 4: ©istockphoto.com/Brad Martin. Page 4: ©istockphoto.com/crisod.

AcknowledgementsWe wish to thank Rene Dekeling of the Ministry of Infrastructure and the Environment, Netherlands, and Mark Tasker of the Joint Nature Conservation Committee (JNCC), UK, for their input to this report. Final responsibility for the content and accuracy of the report, however, lies solely with the author.

Corrigenda

This version of the report, published on 30 October 2013, replaces the earlier versions published on 2nd September 2013 and 28th June 2013. Following consideration of comments received on the Underwater Noise Future Brief, elements of the text have been modified as follows:

Amendments made on 30 October 2013:

Section 1, Types and sources of underwater noise, page 4. This has been amended to acknowledge that "mid frequency naval sonar may be harmful to marine mammals".

Section 2.1. Physical damage, page 4. To better reflect the scientific consensus, the second paragraph has been revised. It draws attention to research (Frantzis, 1998) that indicates that noise produced by military sonar can cause stranding in beaked whales and provides information taken from a report by the International Council for the Exploration of the Sea (2005) on the possible mechanisms that may lead to stranding.

Amendments made on 2nd September 2013:

Introduction, page 3. To acknowledge existing uncertainty surrounding the evidence, the statement ‘Currently these requirements pose a challenge, particularly considering the limited evidence on sounds impacts” has been changed to: ‘Currently these requirements pose a challenge, particularly considering the difficulties of generalising based on existing evidence from a range of different species and noise sources.”

Section 2.4. The balance of effects, page 6. To acknowledge existing uncertainty surrounding the evidence, the statement "As current evidence suggests that noise only rarely kills marine animals, those pressures that do very often kill marine species, such as fishing and pollution, could be considered more important”, has been changed to “As it remains an open question how many marine animals are killed by noise, those pressures that are known to kill marine species, such as fishing and pollution, could be considered more important.”

Summary, page 7. To account for the broad range of noise sources, the statement the summary “Underwater noise from shipping, energy production, fishing and tourism”, has been modified to “Underwater noise from sources including shipping, energy production, fishing and tourism”.

The following references have been added to support information provided in the report: Frantzis (1998); International Council for the Exploration of the Sea (2005); Løkkeborg et al. (2010).

Introduction

Underwater NoiseThe oceans are increasingly exposed to sounds from human activities, such as shipping and the building of foundations for offshore construction projects. What impact do these sounds have on species that inhabit the marine environment? This Future Brief from Science for Environment Policy explores existing research on the ecological effects of underwater sound. Key gaps in our knowledge are also highlighted, and potential strategies for reducing negative impacts on marine species are outlined.

Underwater noise is an important aspect of the Marine Strategy Framework Directive (MSFD), which aims to achieve good environmental status (GES) of the European marine environment by 2020. Noise is defined here as sound that causes negative effects.

GES is defined according to a set of 11 broad indicators or ‘descriptors’1, including those focusing on biological diversity, fish populations and marine litter. Descriptor 11 focuses on energy inputs, including underwater noise. In February 2012, the MSFD Technical Subgroup on Underwater Noise delivered a report to the European Commission, providing guidance on implementing aspects of the MSFD under descriptor 11 (Van Der Graaf et al, 2012).

Some existing measures indirectly control sound in European waters. For example, permits for pile-driving – the sinking of pole-like foundations – are granted based on Environmental Impact Assessments. In

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addition, under the Habitats Directive, noise is regarded as a disturbance that may have detrimental effects on wildlife, including marine life. In particular, it prohibits deliberate disturbances that affect populations of protected species and their ability to survive, breed and rear their young (European Commission, 2007).

However, as part of the MSFD roadmap, EU Member States will need to address sound more directly and work together in shared waters to achieve GES as defined under descriptor 11. This will involve defining potentially harmful levels of underwater sound, and putting in place monitoring systems (by 2014) and measures (by 2015) that will be needed if underwater sound needs to be reduced. Currently these requirements pose a challenge, particularly considering the difficulties of generalising based on existing evidence from a range of different species and noise sources.

1. http://ec.europa.eu/environment/water/marine/ges.htm

1. Types and sources of underwater noise

Sound travels rapidly through water – four times faster than through air. As in open air, sounds are transmitted in water as a pressure wave. They can be loud or soft, high- or low-pitched, constant or intermittent, and volume decreases with increasing distance from source. Sound pressure is most commonly measured in decibels (dB). Underwater noise (as viewed by the MSFD) has been divided into two main types:

• Impulsive: loud, intermittent or infrequent noises, such as those generated by piling, and seismic surveys

• Continuous: lower-level constant noises, such as those generated by shipping and wind turbines

These two types of MSFD-related noise have different impacts on marine life. In addition, mid-frequency naval sonar may be harmful to marine mammals. The frequency, or pitch, of the noise is also important, as animals are sensitive to different frequencies. For instance, most of the noise produced by leisure boats is low frequency, below 1.5 kilohertz (kHz). Although most sensitive to sounds above 15 kHz, bottlenose dolphins could be disturbed by these boat noises because they hear in the wider range 0.075 - 150 kHz and some calls, thought to be food-related, are below 2 kHz (Rako et al, 2013).

The underwater environment is becoming noisier in some areas as it is increasingly exploited (Subsidiary Body on Scientific, Technical and Technological Advice, 2012). Diminishing resources mean that we are turning to the oceans to generate our energy, by building offshore installations, and to mine precious minerals, and fishermen use sonar to tell them where to fish.

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‘The underwater environment is becoming noisier in some areas as it is increasingly exploited.’

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Studies suggest that the loud noises used by seismic survey ships to map the geology of the oceans and seas can affect the hearing and behaviour of some marine species.

2. Impacts of underwater noise on marine lifeMost of the research on the impacts of underwater noise has until recently focused on marine mammals, such as harbour porpoises. There has been less work to understand its effects on fish and other species.

In theory, the behaviour of any species with the ability to sense or use sound may be affected by manmade noise. However, to what extent, in most cases, remains uncertain. Very loud noises, such as those made by explosives, may result in permanent damage to animals close to the source. Whether a species is affected may also depend on that species’ hearing range. Humpback whales, for example, can hear lower-pitched sounds than killer whales (Southall et al, 2007). There are many difficulties associated with analysing the impacts of noise. For example, it is difficult to understand the severity of effects that noise causes and to identify the level at which these effects become unacceptable. Furthermore, it is difficult to determine exactly which aspects of noise cause adverse effects, for example, whether frequency, repetition rate or other aspects are to blame.

2.1 Physical damage

Studies on underwater noise have established that noise can cause permanent injury in some marine animals (Popper et al, 2005). In the worst cases, physiological damage caused by noise can lead to death. For example, fish with swim bladders are particularly susceptible to loud noises, such as those from pile driving, because the gas in their swim bladders is easily expanded by sound pressure (Jones & Street, 2009). This can cause the swim bladder to rupture.

Mass strandings of marine mammals in the EU, including in Greece, have been linked to military sonar (Frantzis, 1998). Noise produced by military sonar can cause stranding in beaked whales, although it is not entirely clear whether stranding is due to direct physiological effects of noise, or behavioural responses to noise that lead indirectly to stranding (International Council for the Exploration of the Sea, 2005). It has been suggested that if deep-diving whales surface rapidly

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in response to noise from sonar they might suffer bubble-related tissue damage similar to that which occurs in decompression sickness in humans, and that this may lead to stranding.

Noise can also temporarily or permanently damage the structures of the ear. One study found that sonar pulses led only to temporary hearing loss in bottlenose dolphins (Mooney et al, 2009). Unsurprisingly, however, hearing effects vary with the type and level of noise, as well as between different animals. Air gun blasts similar to those used in seismic surveys have been shown to cause temporary hearing loss in northern pike fish, whereas the same blasts had no effect on broad whitefish (Hastings and Popper, 2005). In turn, effects on hearing may affect animal behaviour.

2.2 Habitat displacementExposed to noise, some marine species may move to quieter waters. As with physical effects, understanding the effects of this displacement is important – some animals may return to their former habitats after loud, impulsive noise, some may be permanently displaced by low-level continuous noise, but others may remain unaffected. At present, however, displacement effects have only been observed for a few species in the short term. Longer-term studies that can distinguish between the effects of noise and other stressors are needed.

The range at which sound can affect marine organisms depends on many factors and varies. Madsen et al, (2006) estimated that pile-driving noises should be perceptible by marine mammals over 100 kilometres away, but evidence of displacement of harbour porpoises is limited to 15-20 kilometres. In addition, different noise sources may overlap in their impacts on animal populations.

Danish nature and energy agencies and commercial wind farm companies have been monitoring populations of fish and marine mammals at the Horns Rev and Nysted offshore wind farms since 2002 (Pickaver, 2010; Danish Energy Authority, 2006). The results for harbour porpoises are conflicting, with the population at the Horns Rev wind farm decreasing slightly during construction and then recovering during operation. At Nysted, there was a larger decrease during construction and a slower recovery. Seals appeared only to be affected during the construction phase and fish were affected little overall.

In popular leisure boating areas, animal populations have shown seasonal dips. Research in the northern Adriatic Sea of Croatia between 2007 and 2009 showed that bottlenose dolphin populations in the Cres-Lošinji region declined during the tourist season, between June and September (Rako et al, 2013). The authors of the study linked the dips to continuous low-frequency noise produced by the engines and propellers of leisure boats and suggested that dolphins avoid noisy areas because noise interferes with their ability to communicate.

Studies on responses to underwater noise in fish suggest that loud noises made by airguns in seismic surveys can affect behaviour, although real impacts in the marine environment are difficult to measure. A 2012 experimental study conducted in sea cages found that fish swam faster in response to air gun noise, in tighter schools and closer to the bottom

of cages (Fewtrell and McCauley, 2012).

Less information on the effects of noise is available for marine invertebrates, such as squid. However, Fewtrell and McCauley (2012) also noted that squid jetted away from airgun noise, suggesting they would have left the area if they had not been confined by cages. They also released ink, a potential alarm response. In follow-up trials, the same animals became less responsive to airgun noise, but it is not clear whether this was due to hearing damage or to the animals becoming accustomed to the noise.

As part of the European Commission-funded project AQUO2, 13 European partners will assess the impact of shipping noise on marine life, by linking noise maps to migration of marine species (Quiet Oceans, 2013).

2.3 Hunting and communication disturbancesEven at significant distances, it is thought that manmade noises may alter animal behaviour by masking the sounds made by the animals themselves. For example, noise from whale-watching boats may interfere with killer whale calls up to a distance of 14 kilometres (Richardson et al, 1995). Marine mammals, such as whales and dolphins, use sound to hunt, communicate and navigate, for example, using high-pitched clicks that bounce off their prey. Interference with these signals by manmade noise is termed ‘masking’. Masking occurs at different frequencies, with each species having its own critical range of frequencies and levels, depending on the type of sounds used by the animal (Reichmuth, 2012).

One study used modelling to estimate the impact of communication masking caused by shipping noise on fin, humpback and right whales, based on noise data collected in whale habitats in the Gulf of California and Mediterranean Sea (Clark et al, 2009). Shipping noise was predicted to affect the endangered North Atlantic right whale more severely because its calls are quieter. However, more research on the variability and meaning of whale calls is needed to fully understand the impact of shipping noise, including its potential implications for social bonding, mating and feeding.

It is unclear to what extent marine animals are able to overcome masking noises, for instance, by altering their calls. In addition, the masking effects of high-frequency sounds, such as those from echo-sounders and sonar systems, are highlighted as a key knowledge gap in the report of the Technical Subgroup on Underwater Noise (Van Der Graaf et al, 2012).

‘Exposed to noise, some marine species may move to quieter waters.’

2. http://aquo.eu

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2.4 The balance of effects

Because the effects of noise interact, it can be difficult to differentiate between the impacts of noise on marine species. For example, changes in behaviour may be caused directly by noise, or caused indirectly by physical damage arising from noise that leads to an inability to perceive communication calls or detect prey. It might be that prey distribution is affected, reducing the ability of predators to forage effectively.

Researchers who mapped the underwater noise environment near a fuel receiving facility off Sha Chau Island in Hong Kong highlighted the difficulty of understanding the impact of tanker noise on dolphins in the region (Würsig and Greene, 2002). It was unclear whether the dolphins had adapted to the noise, whether their hearing had been damaged, whether important communication signals were being masked, or whether noise even had an impact at all.

Separating the effects of noise from other environmental disturbances can also be complex. According to Pickaver (2010), for example, the cables that carry electricity to the shore at offshore wind farms produce an electromagnetic field that some fish may avoid. In addition, the displacement of one species could indirectly trigger the disappearance of predators or an increase in prey.

The impacts of noise must be viewed in a wider context, considering how the effects of noise on populations compare to those of other human pressures on the marine environment. As it remains an open question how many marine animals are killed by noise, those pressures that are known to kill marine species, such as fishing and pollution, could be considered more important. It is also debatable whether habitat displacement is a negative impact, particularly when resources such as food and space are abundant.

3. The ultimate effects of underwater noise on people and society

The human impacts of environmental change are often understood in terms of ecosystem goods, such as fish stocks used by humans for food, and ecosystem services, such as tourism. Both of these examples are relevant to underwater noise, which affects fish populations and may have implications for tourism associated with whales and dolphins. At present, however, there is little evidence to guide our understanding of the direction or magnitude of any effect, with studies focusing on the most sensitive species, rather than commercially important.

The results of research funded by the Norwegian Petroleum Directorate in 2009 suggest that noise from seismic survey guns both increased and decreased fish catches off Vesterålen, Norway, depending on the species and fishing method (Løkkeborg , 2010). Noise may have driven Greenland halibut into nets, thus increasing catches. On the other hand, pollack and line-caught halibut catches were reduced during the surveys.

4. Monitoring underwater noisePrior to the MSFD, the law did not explicitly compel EU Member States to monitor underwater noise. However, Member States will need to coordinate their efforts to ensure that appropriate systems are in place in shared waters by the MSFD deadline in 2014.

Appropriate technologies and methods for monitoring are available, but a number of issues still need to be resolved for monitoring to be effective. For instance, there are different ways of measuring and expressing noise, and for comparison at national, European and international levels, data must be consistent. In addition, to avoid high economic costs, the level of detail must be balanced against coverage (Van der Graaf et al, 2012). In 2012, the MSFD Technical Subgroup

on Underwater Noise proposed compiling a database of loud impulsive noises likely to cause significant impacts on marine animals, potentially in an EU-wide noise register. Guidance on measuring noise and interpreting noise data is currently being developed.

As part of the EU LIFE-funded project ‘Baltic Sea Information on the Acoustic Soundscape’ (BIAS), partners in Denmark, Estonia, Finland, Germany, Poland and Sweden are collaborating to create a sound map of the Baltic Sea via 40 noise monitoring stations (SYKE, 2013). The project aims to define Good Environmental Status, as required under the MSFD roadmap, and refine a measurement system for monitoring underwater noise.

Dolphins use sound to hunt, communicate and navigate, but manmade noise may be interfering with these signals.

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5. Reducing the impact of underwater noise

According to Parsons et al (2009), the simplest way to reduce the impact of underwater noise on marine life is to avoid carrying out noisy activities where and when noise-sensitive species are present. In practice, this is not always feasible, owing to competing interests, such as the need to generate renewable energy and income from tourism, and limited knowledge about the distribution of marine species. Risk mapping can provide information to aid in the avoidance of important habitats. However, weighting of the importance of sensitive species will determine what impact is considered acceptable.

One recent study in the Mediterranean sought to understand whether models based purely on environmental characteristics could be used to accurately map beaked whale habitats without carrying out surveys (Azzellino et al, 2011). The researchers argue that their predictions were of acceptable accuracy and suggest that risk maps generated through the same approach could be used to minimise noise impacts on beaked whales.

Alternative technologies and construction techniques can directly reduce the noise associated with human activities. Floating wind farms

can avoid piling, while air bubbles that absorb or deflect sound waves and alternative piling hammers may help reduce piling noise. In 2009, the California Department of Transportation reported successfully employing air bubble ‘curtains’ to reduce noise from piling during bridge construction projects and protect fish (Reyff, 2009). There are further challenges associated with pile driving in deeper water or at higher current speeds. In addition, many ‘solutions’ may be costly in relation to other measures likely to improve the welfare of the species being affected.

Noise generated by boats is associated with moving parts in the engine, flow around the hull and with ‘cavitation’ (the creation and collapse of bubbles) caused by the rotation of propellers (Rako et al, 2013). Driving at the ‘design speed’ can help reduce noise.

Some countries also recommend ‘soft-start’ approaches that progress from quieter to noisier activity, for instance, in sonar and seismic surveys, and that noise activities are carried out in the presence of a trained marine mammal observer.

6. Knowledge gaps

Noise is just one of many pressures faced by marine species. Future studies will improve our understanding of the effects of underwater noise and its importance in the context of an environment that is already at risk from other manmade threats. Key knowledge gaps include:

• Doesnoisematterifanimalsremaininnoisyareasorleavebut later return?

• Whatarethecumulativeeffectsoflessfrequent,loud, impulsive noise?

• Howstrongaretheeffectsoflow-level,constantnoiseon habitat displacement?

• Towhatextentareanimalscapableofadaptingtonoise?

• Howarelesswellstudiedspeciesaffectedbyunderwaternoise?

Summary

Underwater noise from sources including shipping, energy production, fishing and tourism has been found to affect the marine environment in various ways. Impacts on species, including marine mammals and fish, range from permanent physical damage to temporary displacement from an area. However, for many species, the nature and severity of effects remain uncertain and unproven. In particular, further research is needed to understand the long-term impacts of loud, infrequent noises and low-level continuous noise on marine life.

‘There is... growing concern of the cumulative effects of anthropogenic sound and other stressors and how this can affect populations and communities... The additional threat of living in a noisy environment may push already highly stressed marine animals into population decline with subsequent effects on marine communities and biodiversity.’Convention on Biological Diversity report (2012)

The MSFD will soon require EU Member States to have strategies in place for monitoring and, where necessary, mitigating underwater noise. To inform these efforts, the best available evidence in this developing field will need to be used, and efforts in shared waters must be coordinated. There is a need to define harmful levels of noise and protect the most sensitive species.

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