Understanding Anthropogenic Underwater Noise
Sources of anthropogenic (human-caused) underwater noise have increased significantly over the past fifty years, largely as a result of increases in seismic exploration, military and commercial sonars, and maritime transportation.
Commercial shipping is one of the main contributors to anthropogenic noise and is mainly generated by propeller cavitation and onboard machinery. The low-frequency sounds that ships generate propagate efficiently and travel vast distances in deep water marine environments. In the open waters of the North Pacific Ocean, acoustic tracking indicates that low frequency noise, < 80 hertz (Hz), has increased by 10 to 12 decibels (dB) since the 1960s, which coincides with the doubling of marine traffic. This has sparked concerns about the impacts of underwater noise on marine life, which use sound to communicate, navigate, feed and reproduce.
Recognizing that scientists and the international community worldwide have identified that noise has short and long-term consequences on marine life, the International Maritime Organization (IMO) ratified voluntary guidelines in 2014 to address the adverse impacts of shipping noise. These guidelines describe steps to reduce noise emitted by commercial ships. As an IMO signatory and the agency responsible for regulating shipping in Canada, Transport Canada (TC) considered it essential to better understand the problem of underwater noise within Canadian waters. It is within this context that TC contracted the Green Marine Management Corporation to:
- Prepare a detailed summary regarding this emerging issue and its impacts on marine life;
- Describe how commercial shipping contributes to ambient noise in the ocean;
- Identify the main sources of noise produced by ships;
- Compile the main global initiatives addressing issues related to underwater noise;
- List the various workshops/conferences held internationally on the subject in recent years;
- Report on research projects being conducted across Canada on underwater noise;
- Highlight future research needs to properly evaluate the impact of anthropogenic underwater noise on marine life; and
- Develop a list of recommendations in collaboration with industry partners and non-governmental organizations (NGOs) regarding the actions required to address the issue.
Assessing commercial navigation’s contribution to ambient underwater noise and its impact on marine life is complex. This report assembles some of the technical knowledge about anthropogenic underwater noise and its potential impacts in a marine environment. It details information about how, based on the current state of knowledge, the maritime industry contributes to ambient underwater noise and should facilitate understanding on how noise can pose a threat to the conservation of marine animals and to the recovery of species at risk.
The Green Marine Management Corporation initiated its research in August 2014 with the ultimate goal of adding underwater noise issue as a new performance indicator within the Green Marine environmental program. A formal working group was created, gathering a number of experts and people concerned or affected by the issue, which include Members of the scientific community (engineers, naval architects, biologists, NGOs and academics), the maritime industry (ship owners, port authorities/administrators and terminal operators) and government agencies (TC and Fisheries and Oceans Canada).
Consultations with scientists and other experts on underwater noise in Canada and the United States helped collate documentation regarding the subject, much of which is included in the reference section. To ensure that the information contained in this report is accurate, all segments have been reviewed by one or more experts. Their names and respective organizations are listed in the Acknowledgement, although Green Marine is responsible for any errors found within this document.
Underwater noise originates from a range of sources – both natural and anthropogenic. A thorough analysis of ambient noise requires consideration of all activities contributing to substantial increases in noise levels, such as industrial activities near or directly in the water, port operations and boating excursions (marina tours, whale-watching cruises, fishing expeditions, research trips, commercial shipping, pile driving, etc.). Sounds of a natural origin should also be considered: cracking ice, wind, waves, rain, thunder, earthquakes, as well as the sounds of marine life. However, it is widely recognized that anthropogenic noise has increased dramatically in recent decades, and is now recognized as a global issue.
To properly evaluate the potential impacts of anthropogenic underwater noise on marine life, it is essential to have a calibrated recording system across a broad range of frequencies to monitor ambient noise in locations considered to be ecologically important. This requires an extensive consultation process with local experts and others with an interest in underwater acoustics.
Behavioural observations of the impact of anthropogenic noise on marine animals are difficult to interpret, and likely not the best metric for impacts. Quantifying the impacts of anthropogenic noises on marine species is complex. Marine animals, regardless of the species, may differ in how they use sound, particularly animals of different age, sex and life stages, auditory systems, hearing thresholds, tolerance to strong noise sources, changes in behaviour and/or hearing resulting from past exposures, and a soundscape’s integral role in the essential biological activities, social interactions and other behaviours of a species.
Identifying acoustic thresholds is difficult, especially in the case of chronic and continuous noises, such as those produced by vessels. When it comes to strong pulsating noises (pile driving, underwater dynamite and other sources), acoustic thresholds can generally be predicted in relation to the known sensitivities of a species by using monitoring auditory equipment. Numerous studies have been done in this regard, and for some species, the acoustic thresholds have been established. For chronic noise, however, the situation differs. Injuries to marine mammals from ship noise are generally indirect, and focus primarily on disturbance, sound masking (which interferes with communication and echolocation), increased stress hormones and, increased in risk of ship strikes.
Underwater noise has been recognized as a major concern for more than ten years in Canada and is identified as a major threat for marine mammals at risk. Therefore, numerous research projects are under way regarding the impacts of noise from vessels on marine ecosystems. Government agencies, universities, engineering firms and NGOs have mobilized to better understand underwater noise, and a large number of hydrophones have been deployed through coastal waters in Canada. To avoid duplicating efforts, it is essential to coordinate initiatives and to archive results.
To request a copy of the full Report, Understanding Anthropogenic Underwater Noise, please contact TDCCDT@tc.gc.ca