Noise Management

Addressing the activities and threats

Introduction

Noise pollution includes any human-created sound that propagates underwater. Sources include motorised vessels, and underwater construction of nearshore and offshore marine installations, (including marine renewable energy projects). Other major sources are underwater explosions (nuclear and otherwise), shipping, seismic exploration (by the oil and gas industries), and naval sonar operations [1]. Noise may be acute or chronic, varying in frequency, volume, duration, ‘rise time’ and repetition rate.
Sea Lions © Amanda Cotton

Impacts of noise on marine mammals

Marine mammals, and particularly cetaceans, with their reliance on hearing as their principle sense for navigation, communication and/or hunting, can be extremely vulnerable to anthropogenic noise. These effects can include hearing impairment, stress, and changes in behaviour from acoustic ‘masking’ (obscuring important natural sounds) [1].

Chronic shipping noise is known to interfere with marine mammal behaviour, and lead to hearing loss, stress, difficulty feeding, mating disruption, stranding, and mortality [6], while acute, high-intensity sound exposure (i.e. high-intensity sonar or airguns) has led to the mass-stranding of beaked whales. Different baleen whale species have shown a variety of responses to different anthropogenic sounds [2].

Management strategies to minimise the impacts of noise

*Note; many of these management strategies may fall under the partial or full jurisdiction of agencies other than MPA management.

Given that the impact of noise on marine mammal species varies between species, the type of sound and the location, a variety of strategies may be appropriate in order to reduce these impacts in different MPAs. Furthermore, due to sound travelling much further and faster in water than in air, acoustic buffer zones may need to be outside MPAs to reduce the impacts of noise [3].

To incorporate management actions to protect marine mammals from noise pollution, legislative responsibility must clearly fall on either MPA management and/or national or regional agencies and be enforceable. Underwater noise limits should also be invoked within the permit process.

Specific management strategies include monitoring (and if possible, maintaining) the status of a species, monitoring the consequences of activities, and incorporating these results into future management plans [4].

Specific management regulations might involve (depending on the species and sources of noise) prohibition of certain sources of noise (such as seismic surveys), regulations specific to seasons or important life history locations, maximum acute noise limits for marine construction and maximum allowable limits to chronic ambient noise for fixed sources. An MPA may also develop strategies to reduce the impact of commercial vessel noise on marine mammals.

Various mitigation technologies may be regulated within the MPA, including the use of alternative reduced noise technologies, and technologies that reduce the noise emitted during conventional shipping or engineering projects. Acoustic Mitigation Devices (AMD) may be employed to drive cetaceans away from specified areas. Monitoring devices can also be deployed. Acoustic hardware can be used for implementing both passive and active acoustic monitoring and noise monitoring programs. Both fixed and towed hydrophones fall into this category [5].

Case study

Stellwagen Bank National Marine Sanctuary (SBNMS) (USA)

The 22 species of marine mammals found in SBNMS are vulnerable to noise from a variety of sources, including large and small commercial vessels, private vessel, aircraft, and industrial development. The goal of minimising behavioural disturbance to marine mammals by noise is explicitly stated within the 2010 management plan.

Within this goal, high-priority strategies include the development of a cooperative marine acoustics research program, and a policy framework for investigating and mitigating noise impacts within SBNMS. Substantial innovative research has been (and continues to be) undertaken into all aspects of underwater noise and its effects on marine mammal species in the sanctuary. However, to date, there is no specific regulation of noise in the MPA, either on-water or from aircraft. However, management actions for the purpose of vessel-strike mitigation, such as rerouting the shipping channel, 10 knot speed restrictions, and passive acoustic monitoring are all likely to result in incidental noise-related benefits.

U.S. Department of Commerce. National Oceanic and Atmospheric Administration. Office of National Marine Sanctuaries. 2010. Stellwagen Bank National Marine Sanctuary Final Management Plan and Environmental Assessment. Silver Spring, MD.

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