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Scotland's Marine Atlas: Information for The National Marine Plan

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CASE STUDY - UNDERWATER NOISE

Why is underwater noise a problem for marine life?

For most marine mammals, many marine fish, and perhaps some shellfish sound is important for communication, locating mates, searching for prey, avoiding predators and hazards, and for short- and long-range navigation. Noise at inappropriate volume and frequency can mask biologically relevant signals; it can lead to a variety of behavioural reactions; and, at very high levels, hearing organs can be adversely affected and, in extreme circumstance, sound can injure or even kill marine life. The total amount of man-made sound has been increasing globally and is likely to go on increasing in Scottish waters in association with increasing offshore industrial activity. Sound produced at low frequencies could have effects well beyond Scottish waters.

Sources of underwater noise

Sound sources of primary concern are explosions, shipping, seismic surveys, offshore construction and offshore industrial activities and sonars of various types, including military sonar, which has previously been implicated in deaths of beaked whales. The cumulative effects of many different sound sources are difficult to predict but are likely to be a challenge to some marine wildlife.

Impacts of underwater noise

There is currently not enough evidence to provide a quantitative assessment of underwater noise in UK waters, but increasing activity in constructing, for example, offshore wind farms, is likely to have raised local noise levels while the developments were underway. Other types of renewable energy systems can also add significantly to the level of man-made sound. The management of subsurface noise emitted from shipping is currently the subject of international debate within the International Maritime Organization and further guidance on this issue is expected in the future.

There is a need to develop effective systems for monitoring noise, and this needs to be accompanied by studies that quantify the related risks to the marine environment.

Variations in underwater noise

The range of frequencies of underwater noise that can be heard by fish and marine mammals and the overlap with the frequency of underwater sound produced by different types of man-made sound sources and weather, including wave and wind noise, are shown in the diagram.

Sources and impacts of underwater noise

Source

Effects of greatest concern

Vessels

Masking
Habitat displacement

Air guns

Masking
Physical trauma
Hearing loss
Behavioural change
Habitat displacement
Behaviourally-mediated effects

Intense low-or mid-frequency sonar

Physical trauma
Hearing loss
Behavioural change
Behaviourally-mediated effects

Pile driving

Physical trauma
Hearing loss
Behavioural change
Behaviourally-mediated effects

Other sonars (depth sounders, fish finders)

Masking
Hearing loss
Behavioural change
Behaviourally-mediated effects

Dredges

Behavioural change
Behaviourally-mediated effects
Habitat displacement

Drills

Hearing loss
Behavioural change
Behaviourally-mediated effects

Bottom towed fishing gear

Behavioural change
Behaviourally-mediated effects
Habitat displacement

Explosions

Physical trauma
Hearing loss
Behavioural change
Behaviourally-mediated effects

Recreational vessels

Masking
Behavioural change
Behaviourally-mediated effects

Acoustic deterrents

Behaviourally-mediated effects

Over flying aircraft (including sonic booms)

Behaviourally-mediated effects

Source: SMRU

Range of frequencies of underwater noise

Range of frequencies of underwater noise

Source: Modified from Slabbekoorn et al (2010) (8)