An Overview Marine Noise Pollution:
Sources, Impacts, and Possible Solutions
Mary Wozny
December 2003
wozny@nova.edu
© Copyrighted, 2003. Do not cite without permission from author.
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Introduction:
In the discussion of coastal policy an important source of pollution is often
disregarded because it is not readily visible. Pollutions such as oil spills, sewage runoff, and
floating debris are all causes for major concern. Chemicals and other toxins entering the
water poisoning our fisheries and damaging our ecosystems definitely need to be addressed
by coastal policies. However, pollutions that cannot be detected by sight alone, including
marine noise, also need to be strongly considered by policy makers. Often, marine noise is
ignored until something visible happens as a result of excessive noise such as the stranding
of whales and other marine mammals.
Marine noise pollution has come to mean any addition to the underwater acoustics
which may interfere with natural processes and harm marine organisms (Brost, Johnson, and
Tulipani 1998). The definition of marine noise pollution does not include natural phenomena
which do contribute to the amount of noise present under the surface of the water. These
natural phenomena can include seismic waves, volcanic eruptions on the sea bottom, breakup
of ice bergs, wind, precipitation, surface waves, and even lightening strikes and meteor
impacts. There are also biological additions to the noise level including sounds produced by
whales, dolphins, fish, shrimp, and other marine organisms (Cromwell, 1998).
Jansey (1999) states that humans have only been a major cause of underwater noise
over the past 150 years. Before that, almost all of the noises heard underwater were produced
by the previously mentioned natural events. However, once industry and science developed
further our affect on the oceans became more apparent. There are estimates that suggest that
the ambient ocean noise rose 10 decibels from 1950 to 1975 alone (Jansey, 1999). This may
not seem like a great increase, but the decibel scale is logarithmic. Therefore, a 10 decibel
increase, increases noise by 10 times. An increase of 20 decibels increases noise by 100
times. Sound also travels much faster and farther underwater, about 5 times faster and it can
travel for thousands of miles (Scowcroft, 2003).
The frequency of noise is also of concern when talking about noise pollution. Jansey
(1999) explains that lower frequency sounds travel farther underwater and are used by
various marine animals to communicate, locate food, and navigate. Low frequency sounds
introduced into the environment can interfere with these animals, especially mysticetes
which tend to communicate with low frequency sounds more often than high frequency
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sounds (Jansey, 1999). Also, decibels drop as sound travels across distances, but frequencies
remain constant (Scowcroft, 2003).
Sources of marine noise pollution:
There are numerous
sources of marine noise
Table 1: Sources of Marine Noise Pollution
pollution. Table 1 shows
(Adapted from Brost, Johnson, and Tulipani (1998) and NOAA)
various sources of marine noise
and the decibels and
frequencies at which they occur.
As can be seen some common
sources of marine noise include
ships, air guns, scientific
research, dredges, fishing
equipment, oil drilling, and
sonar. In order to fully
understand the decibel levels of
common marine noises, Table 2
has been included which
demonstrates the decibels of
sounds we are exposed to on a regular
basis. Table 2 also explains at what levels
humans experience pain, temporary
Table 2: Common noises and their decibel levels
(Adapted from the League for the Hard of Hearing, 2003)
hearing loss, and permanent hearing loss due
to these exposures.
According to Scowcroft (2003), ships
and recreational boats are the source of a
great majority of the noise pollution found
underwater. They create noise from their
propellers, motors, gears, and even from
waves crashing against them as they travel.
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The waves crashing against them create bubbles that introduce additional noise into the
marine environment. As the speed at which a vessel is traveling increases, the amount of
sound generated by that vessel will also increase. Due to the varied types and sizes of the
ships and boats sailing our oceans, innumerable sounds are generated everyday at countless
decibels and frequencies (Scowcroft, 2003).
Commercial fishing activities produce marine noise pollution, not only through their
motors and propellers, but also through the gear they use. Commercial fishermen often
depend on sonar and echo sounders to easily find large schools of fish. However, the use of
these devices may affect organisms other than their target species. Fishermen may also use
devices called acoustic deterrent devices (ADDs) and acoustic harassment devices (AHDs) to
aid in their fishing efforts. According to Preston (1997), ADDs or pingers operate at a
frequency of 130 decibels. They are used with the intention of preventing by-catch. ADDs
emit a sound which causes animals to avoid the nets and other fishing gear in which they
may become entrapped. They have been successful as reducing by-catch, but effects on
hearing are not known. AHDs or ringers as they are commonly called operate at decibels
greater than 190. They are used to cause pain and fear in marine mammals in hopes of
excluding them from particular areas (Johnston, 2002).
Air guns are another source of marine noise pollution. They are often used by oil
companies that are searching for potential oil reserves under the sea floor. Seismic survey
vessels fire a pulse from a gun which travels through the water and hits the sea floor. Once
the pulse reaches the bottom of the ocean, it bounces off and returns to the ship. The way in
which the pulse is returned to the ship and recorded by microphones can be used to
determine what lies beneath the floor of the ocean (Cromwell, 1998).
Scientific research increases the acoustic level of the oceans on a regular basis. One
such project that is currently being conducted is known as Acoustic Thermometry of Ocean
Climate or ATOC (Howard, 1998). The project is utilizing a new way in which to track long
term climate changes associated with global warming patterns. Figure 1 shows some of the
pathways used by the acoustic measurement devices employed by ATOC. These paths travel
distances up to 3,100 miles in the North Pacific and the path to New Zealand covers 6,200
miles. The fundamental principle being used in this study is that sound waves travel
differently through warm and cold water. In warmer water sounds are transmitted faster.
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Therefore, if the oceans are warming up sounds
transmitted from one location will take a shorter time to
reach stations on the other side of the ocean in the future
trials than they initially took. Using this knowledge the
ATOC researchers will be able to track how fast our
planet is warming (Howard, 1998), but the effect of the
ATOC project on marine organisms is currently not fully
understood and is being researched. According to
Howard (1998), only slight changes in the distributions of
such mammals as sperm whales and humpback whales
have been recorded. However, this project is potentially
Figure 1: ATOC Pathways in the Pacific Ocean
(Howard, 1998)
very harmful since it employs the use of low frequency
sounds that sound for twenty minutes, every four hours, on every fourth day (Scowcroft,
2003).
Sonar used by the Navy has become a public concern recently. The Navy uses what
is known as Low Frequency Active Sonar to aid in securing our borders and protecting our
military. As Jansey (1999) describes, the Navy previously used a passive form of sonar. The
Low Frequency Active Sonar is more intrusive and operates at around 230 decibels near the
source and at frequencies ranging from 100Hz to 500Hz. Jansey (1999), states it has been
found that over 300 nautical miles from the origin of the sonar beam the sound level will still
reach 140 decibels, practically the equivalence of standing next to a jet engine (The League
for the Hard of Hearing, 2003). The sonar moves in a sweeping manner throughout the
oceans. The Navy hopes to implement this system of detection throughout the waters of the
world. With the Navy’s Low Frequency Active Sonar and other scientific sonar uses our
oceans may soon be permanently and constantly invaded by these extreme noises.
Oil rigs, deep sea drilling operations, ice breaking ships, etc. are all other forms of
noise that pollute the marine environment. They are capable of producing both low and high
frequencies and decibels. A problem lies in the fact that not every source of marine noise
pollution can be accurately documented. However, it is important that all possible sources be
monitored and successfully managed.
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Impacts of Marine Noise:
When whales and other marine mammals are exposed to loud sounds they may panic.
Breathing rates tend to increase and so does their stress levels (Cromwell, 1998). Other
common effects of exposure to loud marine noise include inner ear damage, hemorrhaging,
impaired hearing, permanent deafness, and disruption of equilibrium. Marine noise,
especially sonar, has been shown to interfere with communication, navigation, hunting, and
mating in marine mammals (Cromwell, 1998). Animals are often forced to find new habitat
due to the degradation of their environment and increases in stress levels may actually
shorten the life expectancy of the affected animals (Jansey, 1999).
Wardle et al. (2001) performed a study in which they fired off seismic air guns to
determine whether marine fish and invertebrates on an inner reef were affected. They found
that these fish did not appear to be highly impacted by the firing of the air gun. The fish
were momentarily disturbed immediately following the firing of the gun, but then retu rned to
their normal behavior. However, they concluded that this will not apply to all fish and the
distance from the firing may have played a role in the response of the fish. It has been
shown in other studies that air guns, as well as other forms of marine noise, can cause
damage to sensitive hearing organs including otolith haircell beds, semicircular canals, and
swimbladders (Wardle, 2001). The damage done to hearing organs can cause a noticeable
disorientation in fish and marine mammals.
Acoustic harassment devices (AHDs) used by fishermen and aquaculturists have been
found to exclude some marine mammals from important habitats (Johnston, 2002).
According to a study performed by Johnston (2002), harbour porpoises in the Bay of Fundy,
Canada were kept out of nursing and feeding grounds by salmon aquaculturists who wanted
to protect their fish from harbour seals and grey seals. This can have long term detrimental
effects on marine mammal populations. AHDs have also been found to drive animals out of
their habitat, forcing them to find new feeding and calving grounds. Jansey (1999), reports
that seals, porpoises, and other cetaceans have been driven up to two miles away from their
original habitat by single AHDs.
Sonar in general has been shown to have many harmful effects on marine organisms.
For example, Brost, Johnson, and Tulipani (1998) indicate that sonar can cause marine
organisms to display avoidance behavior. Researchers played back sonar noise in the
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vicinity of humpback whales and recorded a significance alteration of behavior. The whales
changed their route in order to completely avoid the sonar. Low frequency sonar like the
type the Navy utilizes operates at the same sound level as many marine mammals (Kaufman,
2003). It has been shown to cause sperm whales and belugas to become silent. This means
that the animals temporarily no longer communicated with each other (Jansey, 1999).
Vocalizations sometimes did not return, possibly due to a loss of hearing. Jansey (1999) also
states that the sperm whales and belugas would often stop activities such as feeding and
scatter until the noise produced by the sonar ceased. Aggressive behavior exhibited by the
whales was another reaction that was contributed to the sonar (Jansey, 1999).
Navy operations have been thought to cause mass strandings of whales and dolphins
around the world (Kaufman, 2003). According to Jansey (1999), strandings in the Canary
Islands, Bahamas, Australia, and other locations have been connected to low frequency
active sonar tests performed by the Navy. Kaufman (2003) discusses research that suggests
the low frequency active sonar results in whales and other marine mammals suffering from
the decompression sickness or the bends. The noise may startle the animals so much that it
causes them to rise to the surface too quickly resulting in the formation of excess nitrogen
bubbles in their tissues. Another possible explanation for the presence of nitrogen bubbles in
marine mammal tissues is that the sonar affects gas nuclei that are already saturated with
nitrogen and in the tissues of the animal (Kaufman, 2003). The condition may result in death
as found in the Canary Islands. In total, fourteen beaked whales died in that stranding and
the cause of death for ten of those was linked to a condition similar to decompression
sickness (Kaufman, 2003).
It has been demonstrated that various species of whales will avoid sounds between
110 and 120 decibels (Brost, Johnson, and Tulipani 1998). Most whales studied will avoid
sound levels of 115 decibels. Brost, Johnson, and Tulipani (1998) showed that at 120
decibels gray whales will alter their migration routes by at least a mile. Also, when high
frequency sounds were introduced into an environment almost all whales species in the
vicinity showed some signs of stress. Some became frantic and their heart rate increased. In
others, vocalizations ceased (Jansey, 1999).
The impacts of whale watching vessels are currently being studied in various
locations. Whale watching trips are meant to promote the conservation of marine mammals
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and our oceans, but they may actually be adding to the list of threats against them. Au and
Green (2000) studied the impact of whale watching vessels on humpback whales in the
waters surrounding the Hawaiian island of Maui. In this study the vessels did not hugely
impact the humpback whales. Some whales did demonstrate typical avoidance behavior
while others seemed unaffected by the approaching boats. The reasoning behind this may be
that the boats are required to turn their engines off within a certain distance of the whales and
therefore the whales are only exposed to the loudest sounds for a short period of time. Major
auditory impact is not predicted in this particular environment (Au and Green, 2000).
Humans are also potentially at risk of suffering from exposure to marine noise
pollution. Brost, Johnson, and Tulipani (1998) mention how several divers have documented
incidents in which they feel exposure to extreme marine noise caused them harm. One diver
in 1998 was exposed to a 125 decibel sound briefly while scuba diving. It is believed that
this sound came from tests being conducted by the Navy over 100 miles away. She
complained of disorientation and was diagnosed with a condition known as vibrating lungs.
Preston (1997) states that the Naval Health Research Center found that after 24 hours of
exposure to low frequency sounds at 77 decibels humans (the naval officers exposed) had
adverse health effects and demonstrated significantly lowered performance skills and morale.
There are obviously numerous detrimental effects on marine organisms caused by
marine noise pollution. The effects have been shown to range from simple avoidance
behavior to the death of the organism. Marine noise can severely alter critical habitats and
further threaten already endangered animals.
Acoustic Hotspots:
Acoustic hotspots are similar to biodiversity hotspots; they follow the same concept.
According to Jansey (1999) and the National Resources Defense Council, acoustic hotspots
are places of ecological significance that are already exposed to high levels of man -made
noise. These ecologically significant places include mating ground, nursery areas, feeding
grounds, and any other critical habitats. In 1995, a committee called the National Research
Council was appointed to conduct research in these areas and develop ways in which the
damage done by marine noise can be dramatically decreased. The committee created a list of
hotspots that are being critically threatened by marine noise pollution. Table 3 was created
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in order to represent some of the areas identified as hotspots, the species affected, and the
main sources of noise pollution in the corresponding locations. The species listed in red are
considered endangered or threatened.
Table 3: A Modified List of Acoustic Hotspots (adapted from the Natural Resources Defense Council, Jansey, 1999)
List of Acoustic Hotspots
Location
Adjacent coast
Local species of concern
Human sources of local sound
Bay of Fundy
New Brunswick &
Nova Scotia
Right, fin, and minke whales, harbor porpoise
Shipping, fisheries
Cape Cod Bay
Massachusetts
Right and humpback whales
Shipping, pleasure craft, whalewatching
Cape Mendocino
Northern California
Blue, gray, and humpback whales
Shipping
Eastern/ Southern
Frederick Sound
Southeastern Alaska
Humpback whale
Shipping, fisheries
Great South Channel
Massachusetts
Right, humpback, fin, and minke whales;
numerous odontocetes
Shipping
Gulf of Mexico
Southeastern U.S.,
Mexico
Sperm whale, W. Indian manatee, sea turtles
Shipping, oil/ gas surveying &
production
Gulf of St. Lawrence
Ontario & Nova
Scotia
Fin, minke, blue, and beluga whales
Shipping, whale-watching
Hawaiian Islands
Hawaii
Humpback whale; Hawaiian monk seal
Shipping, dredging, pleasure craft,
ATOC, military activity
Monterey Bay
Central California
Blue, gray, and humpback whales; numerous
odontocetes and pinnipeds
Shipping, pleasure craft, ATOC
North Slope
(Beaufort Sea)
Northern Alaska
Bowhead and beluga whales
Oil/ gas surveying & production
Prince William Sound
Southern Alaska
Gray whale; numerous pinnipeds
Shipping
Puget Sound and environs
Washington &
Vancouver Is.
Gray, humpback, and minke whales; numerous
odontocetes and pinnipeds
Shipping, seismic surveys, fisheries,
military activity
St. Simons Is. to
Melbourne Beach
Georgia & northern
Florida
Right whale
Shipping, dredging, military activity
San Diego Bay
Southern California
Blue, gray, and humpback whales
Shipping, pleasure craft, military
activity
San Francisco Bay &
Farallone Islands
Central California
Blue, gray, and humpback whales; elephant seals
and other pinnipeds
Shipping, pleasure craft, whalewatching
Santa Barbara Channel &
Channel Islands
Southern California
Blue, gray, and humpback whales; elephant seal,
California sea lion, and other pinnipeds
Shipping, pleasure craft, military
activity, oil & gas production
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Policies Incorporating Marine Noise:
All the major policies enacted in the United States that incorporate marine noise
pollution have been reviewed by the National Resources Defense Council (Jansey, 1999).
The National Resources Defense Council examines environmental policies that have been
enacted by the United States and how they can be applied to include marine noise
regulations. It also illustrates problems with the policies and problems in general with
regulating marine noise levels.
The Marine Mammal Protections Act which was enacted in 1972 is examined by
Jansey (1999). Under this policy any activity that may result in harassment, hunting,
capturing, or killing of any protected animal needs to be granted a permit by the National
Marine Fisheries Service or the U.S. Fish and Wildlife Service depending on what species is
being considering. The National Marine Fisheries Service and the U.S. Fish and Wildlife
Service are responsible for deciding whether a proposed project would have more than a
negligible impact on marine species. However, several problems exist with this policy. One
major problem is that there are too many sources of possible pollution to efficiently regulate
them. Also, there are many species adversely affected by noise pollution that are not
protected under the law because they are not marine mammals. The Endangered Species Act
includes some other species, but not all species that are affected by marine noise are
endangered or threatened. These policies allow agencies to subjectively decide what is
negligible and significant.
In 1994, amendments were made to the Marine Mammal Protection Act that both
benefited and potentially endangered marine mammals (Jansey, 1999). One amendment to
the MMPA declared that harassment of marine mammals now included the disruption of vital
activities such as migration, breathing, nursing, breeding, feeding, and sheltering. Any
marine noise that fell under this secondary type of harassment could now be prohibited by
law. However, a second amendment to the MMPA in 1994 also provided an exemption that
could potentially harm marine mammals and other marine species. Congress exempted
fisheries so they could again use their choice of acoustic deterrent devices or acoustic
harassment devices. As previously stated, ADDs and AHDs may prevent marine animals
from utilizing critical habitats. The National Marine Fisheries Service and the U.S. Fish and
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Wildlife Service are responsible for managing the use of these devices, but cannot prevent
the use of them.
Jansey (1999) describes how the Clean Water and Air Act is another policy that is
used to regulate marine noise pollution. Under this policy the source levels of pollution that
are generated are examined. Total noise produced in a region may also be examined rather
than trying to quantify and regulate a single project as called for under the Marine Mammal
Protection Act. However, several problems influence the rate of success of this policy on
marine noise regulation. One issue deals with jurisdiction. The Clean Water and Air Act
does not specifically dictate who regulates regional noise production. Also, fundi ng is an
issue with this policy. Adequate funding is not available to monitor entire regions and
regulate the amount of noise produced.
There are general problems that exist with these policies and others that make an
attempt at managing marine noise pollution. Two of these general problems are regulation
and setting standards. It is difficult to regulate such sources of pollution as the shipping
industry because it is a worldwide industry. Only ten percent of the world’s large
commercial vessels are American-owned. Only two percent are American-registered. It is
impossible for us to enforce regulations unless every country is willing to comply. Others
sources of pollution are just as improbable to manage. Ambiguity in the laws provides
another problem for regulation. Phrases such as “negligible impact” and “harassment” can
be subjective. There are no clear rules set forth to follow. Very few definitions used in
environmental policies are absolute.
Setting standards for noise pollution laws is also impracticable. There is a wide
variation in the hearing ability of animals across different species. Different species are
impacted dramatically by certain noises, while others does not appear to be adversely
affected at all. The location of the animals may also play a role in how they are affected by
different noises. Realistically speaking it would be impossible to set standards for what level
of noise is acceptable. Each case needs to be examined individually.
Conclusion:
Marine noise pollution is finally gaining the recognition as a severe problem that it
deserves. It can no longer be ignored by policy makers. Too many animals are suffering
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needlessly from noise that we add to their environment. Organizations such as the National
Oceanic and Atmospheric Association (NOAA) are beginning global efforts to study noise
pollution. NOAA has a program called Sound in the Sea through which it hopes to
successfully research the sources and impacts of noise pollution on marine animals (Fox,
2003). Sound in the Sea plans to use hydrophones and other acoustic technology to monitor
the sounds that are being produced everyday around the world (Fox, 2003).
Many other things need to be done in order to begin to limit the noise we are adding
to the oceans. Acoustic hotspot monitoring has to be conducted thoroughly. “Cooling
down” these areas has become a necessity to ensure the future survival of various marine
species. Another important issue that has been touched upon, but still requires furthe r
research, is the effect of whale watching boats and other conservation efforts on noise
production. If conservation efforts that have been implemented are adding to the noise
pollution problem they need to be reassessed.
Right now we know too little about marine animal hearing abilities so it remains
impossible to set any standards that can be upheld. Therefore, we need to increase the
number of locations that are currently being studied and also increase the number of
researchers that are involved. This will include giving more funding to the researchers
currently involved with noise production projects. Shipping regulations need to be updated
and enforced worldwide. Even cruise ships need to be assessed and updated if they are found
to be creating too much underwater noise. Exemptions for the Navy, fisheries, and other
groups need to be reexamined and only issued in absolute dire situations. Marine noise
pollution, as with any other pollution problem, will only be successfully managed and
regulated if national and worldwide organizations cooperate to benefit the environment.
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Brost, B., Johnson, B., and D. Tulipani. 1998. “Underwater Noise Pollution and Marine
Mammals.” Biology of Marine Mammals.
http://kingfish.coastal.edu/marine/375/noise.html
Cromwell, D. 1998. Noisy Oceans. Science Tribune. 2pp.
Fox, C. 2003. Sound in the Sea. Acoustic Monitoring Project, NOAA Pacific Marine
Environmental Laboratory
http://oceanexplorer.noaa.gov/explorations/sound01/background/plan/plan.html
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