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244 | The risks
The marine environment is an
excellent guide to sound waves, which
can propagate over hundreds of kilo-
meters, whereas light penetrates only
a few meters. Many marine species
exploit this property of the ocean to
communicate, locate or spot their
prey. Underwater noise pollution
caused by human activities can
endanger the health of ecosystems,
whose scales of adaptation are not
always as rapid as the changes under-
gone by our
societies.
Sound diversity
A wide range of natural sounds
is emitted in the marine environ-
ment, for example, by geophysical
phenomena. To this geophysical
chorus must be added the biological
chorus generated by living organisms.
Whales sing at low frequencies and
these sounds can spread over several
hundred kilometers. Dolphins whistle
and ’sound’ their surroundings with
specic signals called ‘echolocation
clicks’. Other species emit sounds
of all kinds, such as grunts or snaps.
Many listen to their environment
to communicate, detect prey or ee
predators. Living organisms can also
produce incidental sounds by moving
and
feeding.
Through their offshore activi-
ties, humans add their contribution
to natural submarine soundscapes. e
use of underwater sound sources has
become widespread for seismic pros-
pecting, the detection of objects, esti-
mating sh stocks, measuring ocean
depth, submarine communication...
e lower the frequencies and the
greater the power of the sound source,
the greater the propagation distances.
Moreover, many human activities are
also noisy by nature. For example, ves-
sels and powered vehicles are sources of
noise that emit continuously over time
mainly at low frequencies. Works at
sea, such as those related to the deve-
lopment and exploitation of renewable
marine energies, also generate noise
in the marine
environment.
The study of sounds
Sounds are dened by their dura-
tion, their frequencies and their level,
the latter being expressed in loga-
rithmic scale, the decibel (dB). Two
sources with the same level of sound
do not produce twice as much per-
ceived noise; conversely, the arrival
of a source in a quiet place can consi-
derably increase the perceived
noise.
Underwater acoustics provide two
essential tools for understanding the
risks of noise pollution in the marine
environment. e rst is the observa-
tion of the sounds in the environment
by submarine microphones, called
hydrophones. These instruments
measure the under water sounds-
capes, their temporal dynamics, their
volume, and their frequency content
(Fig. 1). They make it possible to
compare the anthropic and natural
components of the soundscapes in
the same space of representation.
However, considering the extent of
maritime spaces and the propagation
distances of sound waves, hydrophone
observations can only provide sparse
one-o observations. is is why the
15. Ocean noise pollution
Yann Stéphan, Florent Le Courtois and G. Bazile Kinda
16000
14000
12000
10000
8000
6000
4000
2000
00 5 10 15 20 25 30 35 40 45 50
t (s)
f (Hz)
Fig. 1 – Example of time-frequency representation of a recording. The
image makes it possible to estimate the signal frequency content as a function
of time. The figure shows the whistles emitted by dolphins at high frequencies
(above 8000 Hz) and signals emitted by the acoustic sources used in acoustic
oceanography (under 2000 Hz). Source: Shom.
Ocean noise pollution | 245
use of a second tool, spatial modeling,
is essential. is enables noise levels
to be estimated at the ocean basin
scale (Fig.
2).
Too noisy an ocean?
Mass marine mammal strandings
are a very strong ecological symbol,
although the causes of such events are
rarely precisely known. For beaked
whales, more than 90% of mass stran-
dings reported since the end of the
19th century took place aer 1950;
this period was marked by the deve-
lopment and intensication of the use
of high-power sources, particularly in
underwater warfare (sonars) and oil
prospection (air guns). In particular,
the linking of mass strandings with
nearby naval exercises made it possible
to formulate the rst hypotheses of
the traumatic impact of impulsive
sources of human origin. e autopsy
of animals stranded in the Canary
Islands in September 2002, during
an international military exercise,
revealed lesions likely to be directly
linked to decompression accidents, as
well as acoustic
trauma.
At the same time, the level of
ambient noise is changing with the
increase in maritime trac. Several
studies have compared the probabi-
lity of stress in some whales caused
by the noise of vessels. e risk of
masking animal communications
by boat noise is also an important
issue. Changes in marine mammal
vocalizations in terms of levels,
durations or frequencies over several
years of recordings were attributed
to ambient anthropogenic
noise.
A new environmental
challenge
e eort of scientic research
and the accumulation of knowledge
have made it possible to publish
increasingly urgent alerts on noise
nuisance on marine life in general.
ese are beginning to be taken into
account by environmental policies.
In 2008, the European Commu-
nity introduced underwater noise
pollution into the Marine Policy
Framework Directive. Implementa-
tion of nuisance risk management
protocols, such as animal presence
monitoring protocols, the so start
of sound em issions or acoustic
damping have become common,
encouraged and even regulated for
certain uses. Other initiatives are
also emerging, such as the incen-
tive recently initiated by the Port
of Vancouver in which quieter ships
pay lower mooring
costs.
The need to maintain anthro-
pogenic noise at levels without risk
to the health of marine ecosystems
places human beings before the
challenge of sound ecology: moving
from the world of silence to that
of
harmony.
References
DCSMM – Stratégie pour le milieu marin, directive 2008/56/CE, 2008.
R. M. SCHAFER Le paysage sonore. Le monde comme musique,
Wild project, domaine sauvage, 2010.
60°N
30°N
30°S
60°S
120°W 120°E High
levels
Sea
noise
Average
levels
60°W 60 °E0°W
Fig. 2 – Example of noise distribution of maritime traffic during the month of July 2012 for the one-third octave
centered on 63 Hz. The model is designed to estimate the sound levels produced by traffic and then propagate these
levels at each point of the globe, in order to estimate the sound levels induced by traffic at different distances. Source:
Shom and Lloyd’s.
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