Underwater Acoustics:: Noise and The Effects On Marine Mammals
Underwater Acoustics:: Noise and The Effects On Marine Mammals
Underwater Acoustics:: Noise and The Effects On Marine Mammals
Compiled by
Christine Erbe
www.jasco.com info@jasco.com
Other quantities and their units are derived from these base quantities Harmonics: integer multiples of the fundamental f : 2f, 3f, 4f, ...
via quantity equations.
Period: • duration of 1 cycle : T = 1/ f [s]
peak amplitude
Multiplier Prefixes: period
rms amplitude
1
peak-to-peak amplitude
Prefix Symbol Factor Prefix Symbol Factor Figure 1: A cosine
Pressure Amplitude
0.5 wave having a peak
deci d 10-1 deka da 101
amplitude of 1, a
centi c 10-2 hecto h 102 0 peak-to-peak
milli m 10-3 kilo k 103 amplitude of 2, an rms
micro µ 10-6 mega M 106 -0.5 amplitude of 0.7, a
nano n 10-9 giga G 109 period of 0.25s, and a
pico p 10-12 tera T 1012 -1 frequency of 4 Hz.
0 0.2 0.4 0.6 0.8 1
Table 2: SI Multiplier Prefixes. Time [s]
Acoustic Impedance: •Z = ρc , ρ: density, c: sound speed Acoustic Power: • the amount of sonic energy E transferred
• in air, 0 C: ρ = 1.3 kg/m3, c = 331 m/s => Z = 430 kg/m2s
o (radiated) within a certain time T
• in fresh water, 15oC: ρ = 1,000 kg/m3, c = 1,481 m/s => Z = • Pwr = E / T = I x A
1,481,000 kg/m2s • Pwr [W: Watts]; 1 W = 1 J/s = 1 kg m2/s3
• in sea water, 15oC, 3.5% salinity, 1m deep: ρ = 1,035 kg/m3, c =
1,507 m/s => Z = 1,559,745 kg/m2s Decibel: [dB]
quantifies variables with large dynamic ranges on a logarithmic scale
quantities expressed in dB are referred to as “levels”
20 log10(P/Pref) , Pref = 1 µPa under water
(c) JASCO Applied Sciences 3 4 (c) JASCO Applied Sciences
10 log10(I/Iref) , Iref = 6.5x10-19 W/m2 for a plane wave with Prms = 1 • also called zero-to-peak pressure (Figure 1)
µPa Peak Pressure Level: [dB re 1 µPa]
SPLPk = 20 log10 (max(| P (t ) |) )
Levels in Air vs. Water: Peak-to-peak Pressure Level: [dB re 1 µPa]
• Standard reference level in air: Pref =20 µPa, under water: Pref =1 µPa.
SPL Pk − Pk = 20 log 10 (max( P (t )) − min( P (t )) )
• 0 dB re 20 µPa = 26 dB re 1 µPa, because 20 log1020 = 26
• For 2 sources of equal intensity in air and under water, the pressure
under water is 36 dB greater than the pressure in air: RMS Pressure: •root-mean-square of the time series P(t)
Ia = Iw Pa2/Za = Pw2/Zw Pw/Pa = √(Zw/Za) • useful for continuous sound (as opposed to pulsed)
RMS Pressure Level: [dB re 1 µPa]
20 log 10 ρ w c w ρ a c a = 36
1
SPLrms = 20 log10
T ∫T
2
P (t ) dt
Some dB Mathematics:
How to convert from dB to linear scale: Source Level:
e.g., 120 dB re 1µPa = 20 log10(x /µPa) • acoustic pressure at 1m distance from a point source
What is x? x = 10120/20 µPa = 106 µPa • SL [dB re 1 µPa @ 1m]
Addition of dB (e.g. amplifier gains): • For sources that are physically larger than a few cm (ship propellers,
120 dB re 1µPa + 120 dB = 240 dB re 1µPa airguns etc.), the pressure is measured at some range, and a sound
Addition of dB referenced to absolute values: propagation model applied to compute what the pressure would have
120 dB re 1µPa + 120 dB re 1µPa = 126 dB re 1µPa, because been at 1m range if the source could have been collapsed into a point-
120 dB re 1µPa = 1 x 106 µPa source.
1 x 106 µPa + 1 x 106 µPa = 2 x 106 µPa = 126 dB re 1µPa; absolute • If Pwr is the total radiated source power in Watts, ρ= 1000kg/m3 the
values need to be added in linear space. water density, and c = 1500 m/s the sound speed, then
A doubling in pressure adds 6 dB: SL = 10log10(1012 ρc Pwr / 4π) = 170.77 dB + 10log10(Pwr)
20 log10(2P/Pref) = 20 log10(2) + 20 log10(P/Pref) • A 1 Watt source has a SL of 170.77 dB re 1µPa @ 1m.
= 6 dB + 20 log10(P/Pref)
• SL can also be expressed in terms of sound exposure [dB re 1µPa2s].
A doubling in intensity adds 3 dB:
10 log10(2I/Iref) = 10 log10(2) + 10 log10(I/Iref) = 3 dB + 10 log10(I/Iref)
Sound Exposure Level:
A 10-fold increase in intensity adds 10 dB:
• proportional to the total energy of a signal
10 log10(10I/Iref) = 10 log10(10) + 10 log10(I/Iref)
• for plane waves:
= 10 dB + 10 log10(I/Iref)
Inversion of reference units changes the sign: SEL = 10 log10 (∫ P(t ) dt )
T
2
Pulse Length: For pulsed sound (e.g. airguns, pile driving), Power Spectrum Density:
the pulse length T90% is taken as the time between the 5% and the 95% • describes how the power of a signal is distributed with f
points on the cumulative energy curve. SPLrms90% is computed by • 1. read the signal time series [µPa] in windows of length T [s]; 2.
integrating P2 from T5% to T95%. compute the Fourier Transform [µPa/Hz]; 3. square the amplitudes,
x 10
9 Single Pile Driving Pulse discard negative f, double remaining amplitudes [µPa2/Hz2]; 4. divide
1 by T [=> µPa2/Hz]
Pressure [µPa]
10
2
95 % cumulative E
• Constant bandwidth: All bands are equally wide, e.g. 1 Hz => power
spectrum density.
5
• Proportional bandwidths: The ratio of upper to lower frequency
2
gen
ear e
noi
era ake +
thq
s
l pa
u
tter xplos
120
no
wi ry s
e
nd h
ve
f
no allo
limits of prevailing noise
ise w
ion
in wat
100
er
ffic
t ra
y
av heavy rain
he
80
Figure 4: Percentiles of ambient noise power spectrum densities
measured in tropical water over a 2 month period. Lines from top to se
bottom correspond to the 5th, 25th, 50th, 75th and 95th percentiles. a
sta
e r te
60 s
n ois ate 6
w
ffic p Cato cu
rves
tra dee e 4
in
n ois
w 2
2. Sound Sources ffic llo
40 tra sha 1
in ater
w
a. Natural Sound Sources 0.5
spectrum follows -
seismic survey.
20logf above
−40 The survey
100Hz. Spectral
ship tows both
average spectrum density levels lines at f<500Hz
−20 dB / decade the airgun
−60 (not shown)
array and the
supersede this
receiving
average spectrum
hydrophone
−80 and differ from ship
1 2 3 4 5 streamers.
10 10 10 10 10 to ship.
Frequency [Hz]
L = 175 + 60 log(u/25) + 10 log(B/4) ,
(c) JASCO Applied Sciences 15 16 (c) JASCO Applied Sciences
Airgun:
• underwater chamber of compressed air
• rapidly released air creates oscillating bubble in the water
omni-directional propagating pressure wave
• waveform shows a primary peak (the desired signal for geophysical
profiling) followed by a series of decaying bubble pulses (Figure 8)
• GI guns consist of 2 chambers: a generator and an injector. The
generator is fired first producing the primary peak; the injector is fired
at half the bubble period (Figure 8); this reduces the unwanted bubble
pulse. The spectrum of a GI gun is smoother than that of a sleeve
airgun. Power Spectrum [dB re 1µPa /Hz @ 1m]
10
x 10 Airgun Waveform Airgun Spectrum
200
20
Pressure [µPa @ 1m]
180
2
15
10 160
5 140
0
120
Pressure [µPa]
Pp = 5.24 x 1013 (W1/3 / R)1.13 : peak pressure [µPa] 0
Pressure [µPa]
Vibratory pile driving:
• vibratory pile driver sits on top of pile 0
• consists of counter-rotating eccentric weights, arranged such that
horizontal vibrations cancel out while vertical vibrations get
−1
transmitted into the pile 0 2 4 6 8 10 12 14 16
• less noisy than impact pile driving time [min]
Figure 10: Waveform of impact pile driving recorded at 320m range.
Impact pile driving: Water depth 3m, hollow steel pile, diameter 0.8 m, wall thickness 1.3cm,
• weight hammers pile into the ground driven to 25m below ground, into sandstone bedrock, hydraulic hammer
of 12t weight and 180 kJ energy rating [15].
• different methods for lifting the weight: hydraulic, steam or diesel
• acoustic energy is created upon impact; travels into the water along Figure 11 gives power spectra for a number of anthropogenic sources:
different paths: airgun array 2900 in3 volume, measured broadside [JASCO]; pile
1. from the top of the pile where the hammer hits, through the air, driving 1.5m diameter hollow steel pile, 280 kJ hydraulic hammer [15];
into the water; 2. from the top of the pile, down the pile, radiating icebreaker propeller cavitation during ridge ramming [18]; large vessels
into the air while travelling down the pile, from air into water; 3. [45; 46; 49]; mean of five dredges dredging and dumping [JASCO]; a
from the top of the pile, down the pile, radiating directly into the drilling caisson [JASCO] and mean whale-watching zodiacs [12].
water from the length of pile below the waterline; 4. ... down the Spectra of the pulsed sources (airgun array and pile driving) were
pile radiating into the ground, travelling through the ground and computed over the pulse length T90% (see p. 7) comprising 90% of the
radiating back into the water total energy. All spectra were measured at some range and back-
• In the water, sound is reflected and refracted. propagated to 1m to compute source levels. This method assumes a
• Near the pile, acoustic energy arriving from different paths with point source and thus over-estimates levels that can be measured close
different phase and time lags creates a pattern of destructive and to physically large sources. E.g., in the near field (see Figure 17) of an
constructive interference. airgun array, waveforms from individual airguns superpose
• Further away from the pile, water and ground borne energy prevails. constructively and deconstructively creating spatially variable received
• Noise increases with pile size (diameter and wall thickness), hammer levels (an interference pattern) that are always less than estimated by
energy, and ground hardness. Figure 10 shows how the level increases back-propagating long-range levels. In other words, reported source
as one pile is driven from start to end. levels are useful to predict received levels at long ranges, but
overpredict near-field levels.
(c) JASCO Applied Sciences 19 20 (c) JASCO Applied Sciences
Anthropogenic Noise Spectra airgun array Solutions to the Helmholtz Equation:
Power spectrum density [dB re 1µPa /Hz @ 1m]
1. φ = F(x,y,z)eiφ(x,y,z)
220
pile driving
200
icebreaker F: amplitude function; φ: phase function
large vessels
range-dependent => Ray Theory
2
dredges
180 drilling caisson
whale−watching zodiacs 2. φ = F(z)G(r)
160 F: depth function => Normal Mode equation => Green’s function
G: range function => Bessel equation => Hankel function
140 range-independent => Normal Mode Models,
Multipath Expansion Models, and
120 Fast Field Models
100 3. φ = F(r,θ,z)G(r)
1 2 3 4 F => Parabolic equation
10 10 10 10
Frequency [Hz] G => Bessel equation => Hankel function
Figure 11: Source spectra of anthropogenic sources. range-dependent => Parabolic Equation (PE) Models
c ∂t 2
• c: speed of sound; t: time
RL [dB re 1 µPa]
directional receiver, the following equation has to be satisfied. 160
SL - TL - NL + DIr > DT 150
f = 100 kHz →
Two-way Sonar Equation: 140
For a signal from an omni-directional source to be detected at a 130
directional receiver at the source location after reflection off a target,
120
the following equation has to be satisfied. f = 10 kHz →
SL – 2 TL + TS – NL + DIr > DT 110
100
Transmission Loss: 10
0
10
1
10
2
10
3 4
10 10
5
RL = SL - TL Range [m]
The following equations can be used as a fast and rough estimate for how Figure 12: Geometrical transmission loss for a source of 200 dB re 1µPa @
sound energy dissipates as a function of range R from the source. 1m. In the combined case, the sound spreads spherically until R = H =
100m, and cylindrically thereafter. Spreading loss is f-independent. Thin
lines: Spherical spreading + f-dependent absorption for f = 10kHz and f =
100kHz.
(c) JASCO Applied Sciences 23 24 (c) JASCO Applied Sciences
Molecular Relaxation (Absorption) Loss: Reverberation:
• due to the relaxation of boric acid B(OH3) and • unwanted echoes that limit signal detection or sonar
magnesium sulphate MgSO4 molecules, and the shear & bulk viscosity performance
of pure water • originates from reflection and scattering off the seafloor, sea
•TL = αR surface and volume inhomogeneities
f1 f 2 T S f2 f 2 • can lead to continuous background noise or discrete
α = 0.106 e ( pH −8 ) / 0.56
+ 0 .52 (1 + ) e −z / 6 interferences
f1 + f
2 2
43 35 f 2 + f
2 2
+ 4.9 × 10 − 4 f 2 e −(T / 27 + z / 17 ) The change in the speed of sound with depth distorts the spherical and
1/2 T/26
with f1=0.78(S/35) e and f2=42e ; f [kHz], α[dB/km]T/17 cylindrical wave fronts. This effect is treated by more sophisticated
valid for -6 < T < 35°C (S=35ppt, pH=8, z=0) propagation models.
7.7 < pH < 8.3 (T=10°C, S=35ppt, z=0)
c. RAY Propagation
5 < S < 50ppt (T=10°C, pH=8, z=0)
0 < z < 7km (T=10°C, S=35ppt, pH=8) [1; 24; 25] Reflection: • is the change in direction of a wave at an interface
between two different media so that the wave returns into the medium
from which it originated
• In specular (mirror-like) reflection,
2
10 MgSO
the angles of incidence and
4 reflection are equal: θ1 = θ2
α [dB/km]
depth
critical depth
excess
depth
• negative sound gradient: sound speed decreases with depth => sound
refracts downwards
• positive sound gradient: sound speed increases with depth => sound
refracts upwards
• sound speed in the deep isothermal layer increases by 1.7m/s every
100m in depth
Figure 16: Sound propagation in the winter at mid-latitudes. There is a
SOFAR Channel: duct at the surface, resulting in a shadow zone underneath this layer.
• abbreviation for SOund Fixing And Ranging; Sound from a surface source refracts upwards and reflects off the sea
surface.
• also called deep sound channel;
• horizontal layer of water at the depth where c is minimum;
Convergence Zone: region where ray paths converge
• this depth is called the channel axis;
Shadow Zone: region into which rays cannot enter by refraction
• axis is about 1000m deep at low latitude and reaches the sea surface at alone
high latitude, i.e. the polar regions;
• acts as a waveguide for sound, ‘trapping’ propagation paths.
(c) JASCO Applied Sciences 27 28 (c) JASCO Applied Sciences
Lloyd Mirror Effect: • A less negative sensitivity belongs to a more sensitive hydrophone,
Consider a source under the e.g. a hydrophone with a sensitivity of -180 dB re 1V/µPa is more
water surface (e.g. a ship sensitive than a hydrophone with a sensitivity of
propeller). A ray emitted -200 dB re 1V/µPa.
upwards reflects off the
surface and experiences a Projectors: • convert voltage to a pressure wave underwater
180O phase shift. The • have a transmit sensitivity that depends on frequency
surface-reflected path
interferes with the direct Near Field (Fresnel Zone): Consider the surface of a transducer a
path at any receiver location. series of separate point sources. At any location in the near field of the
The surface-reflected path transducer, the individual pressure waves will have travelled different
can be considered distances, arriving with different phases. The near field therefore
originating from a negative (inverted pressure) image source in air. For consists of regions of constructive and destructive interference. All
horizontal propagation over long ranges, the path lengths of the direct transducers, whether used as hydrophones or projectors, have near and
and surface-reflected paths will be similar and the pressures will cancel far fields.
out. At close ranges, the two rays create a pattern of constructive and
destructive interference. The Lloyd Mirror Effect is assumed to play a The Fresnel Distance is the range from the source beyond which the
role in ship strikes of manatees and other marine mammals that spend a amplitude does not oscillate anymore, but monotonically decreases.
significant amount of time near the surface. Oscillations are only possible as long as the phase difference between
two points on the source surface that are maximally apart is greater than
half a wavelength.
4. Sound Receivers
Examples: • line array: Rff = l2/ λ, where l: array length c. Data Acquisition (DAQ) Boards
• circular piston: Rff = πr2/ λ, where r: radius of the piston • analog-to-digital A/D converters, e.g. digital audio recorders
• airgun array: Rff = l2/ λ, where l: largest active dimension of • have a digitization gain of M [dB re FS/V], where FS is the digital full
the source scale value that is divided by the input voltage Vmax [V] required to
reach digital full scale
Directivity Pattern: • e.g. M = 10 dB re FS/V means that 0.32V input leads to full scale
• angular distribution of projected energy (in the case of projectors) because: 10 = 20log10(x/(FS/V))
• received level as a function of the direction of arrival of the acoustic log10(x/(FS/V)) = 0.5
wave (in the case of hydrophones) x = 101/2 FS/V = FS/0.32V
• depends on the shape and size of the transducer, and frequency; e.g. • The full scale value depends on the number of bits (n) of the A/D
Figure 9 converter. In bipolar mode, FS = 2n/2 = 2n-1.
• omnidirectional: circular pattern; independent of angle • e.g. 16-bit DAQ: FS = 216/2 = 32768, so the digital values will lie
between -32768 ≤ dv ≤ 32767.
Beamforming: For an array of transducers (hydrophones or projectors),
phase or time shifts between the elements can be chosen such as to steer Resolution:
the direction of the main lobe of the overall directivity pattern of the • is the voltage increment from one digital value to the next:
array. ∆V = Vmax/FS
• e.g. for a 16-bit DAQ with Vmax = 10V: ∆V = 0.3mV
b. Amplifiers • This is the smallest voltage and the smallest voltage difference that
Gain: can be resolved. In between values will be rounded, producing a
• G = 20log10(V2/V1), quantization error of ±∆V/2.
where
V1: input voltage; Example:
V2: output voltage
• E.g. hydrophone connected to amplifier & output voltage measured
with voltmeter; then the SPL measured is:
SPL = 20log10(V2) - G - S • SPL = 20log10(dv/FS) – M – G – S , where dv = digital values in the
• If G>0, then the amplifier increases the amplitude. .dat file
• If G<0, this element works as an attenuator, not an amplifier. • If S = -180 dB re 1V/µPa, G = 20 dB, M = 10 dB re FS/V, then SPL =
• E.g., S = -200 dB re 1V/µPa; G = 20 dB: 20log10(dv/FS) – 10 dB – 20 dB – (–180 dB)
SPL = 20log10(V2) – G – S = 20log10(dv/FS) + 150 dB
= 20log10(V2) – 20 dB – (– 200 dB) Divide the digital values in the .dat or .wav files by FS; take 20log10 ;
= 20log10(V2) + 180 dB subtract all gains; that’s your SPL in dB re 1 µPa.
Family BALAENIDAE
Balaena mysticetus Bowhead whale 29
Figure 26: Distribution of Mesoplodon densirostris (=), M. hectori (\\), M.
stejnegeri (//), M. layardii (||), M. peruvianus, M. bidens and M. bowdoini Eubalaena australis Southern right whale 29
(grey). Eubalaena glacialis North Atlantic right whale 29
Eubalaena japonica North Pacific right whale 29
Figure 27: Distribution of Ziphius (=), M. grayi (||), B. bairdii (\\), B. arnuxii
(//), M. carlhubbsi, M. mirus and I. pacificus (grey). Figure 29: Distribution of Caperea (=), E. australis (||), E. japonica (\\), B.
mysticetus (//) and E. glacialis (grey).
Order CARNIVORA: Carnivores (marine) Figure 31: Distribution of true seals: E. barbatus (//), M. leonina (grey, 9),
Suborder PINNIPEDIA: Seals & Sea Lions M. monachus (grey, 10), M. schauinslandi (grey, 11), Ph. groenlandica
(||), Ph. vitulina (dark grey line), Ph. largha (\\).
(c) JASCO Applied Sciences 41 42 (c) JASCO Applied Sciences
Figure 32: Distribution of true seals: C. cristata (||), H. fasciata (\\), H. Figure 33: Distribution of eared seals. Numbers with arrows belong to
grypus (//), M. angustirostris (grey, 8), P. caspica (grey, 17), P. hispida shaded ranges. Numbers without arrows identify breeding sites on
(grey, 18), P. sibirica (grey, 19). Around Antarctica (=): H. leptonyx, L. islands.
weddellii, L. carcinophagus, O. rossii.
Family ODOBENIDAE
Odobenus rosmarus Walrus 34
Family OTARIIDAE (eared seals)
Arctocephalus australis South American fur seal {1} 33
Arctocephalus forsteri New Zealand fur seal {2} 33 Family MUSTELIDAE (marine)
Arctocephalus galapagoensis Galapagos fur seal {3} 33 Lutra felina Marine otter 34
Arctocephalus gazella Antarctic fur seal {4} 33 Enhydra lutris Sea otter 34
Arctocephalus philippi Juan Fernandez fur seal {5} 33
South African & Australian fur 33 Family URSIDAE (marine)
Arctocephalus pusillus
seals {6} Ursus maritimus Polar bear 34
Arctocephalus townsendi Guadalupe fur seal {7} 33
Arctocephalus tropicalis Subantarctic fur seal {8} 33
Callorhinus ursinus Northern fur seal {9} 33 Order SIRENIA: Sea Cows
Eumetopias jubatus Steller sea lion {10} 33
Neophoca cinerea Australian sea lion {11} 33 Family TRICHECHIDAE
Otaria byronia South American sea lion {12} 33 Trichechus inunguis Amazonian manatee 34
Phocarctos hookeri New Zealand sea lion {13} 33
Trichechus senegalensis West African manatee 34
California & Galapagos sea lions 33
Zalophus californianus Trichechus manatus West Indian manatee 34
{14}
Trichechus manatus latirostrus Florida manatee 34
Mysticete Sounds:
6. Marine Mammal Acoustics • sound production mechanism unclear
Ocean water conducts light very poorly but sound very well. => Marine • 2 categories: calls and songs
mammals rely primarily on their acoustic sense for communication, • Calls have been categorized into simple calls (low f < 1kHz, narrow
social interaction, navigation and foraging. Odontocetes have an active band, frequency and amplitude modulated), complex calls
echolocation system aiding navigation and foraging. (broadband, 500-5000Hz, f and amplitude modulated), grunts &
knocks (<0.1s duration, 100-1000Hz), and clicks & pulses (short
a. Marine Mammal Sounds duration < 2ms, 3-30kHz) [5].
All marine mammals emit sound that is produced internally. Other • Songs have been recorded from humpback, bowhead, blue and fin
sounds, that may also take a social or communicative role, are generated whales.
when an animal strikes an object or the water surface. • Humpback song can be broken down into themes, which consist of
repetitions of phrases, which are made up of patterns of units (with
Odontocete Sounds: energy up to 30kHz).
• generated within the nasal system, not the larynx
• can be classified into 3 categories: tonal whistles, burst-pulse sounds Pinniped Sounds:
and echolocation clicks • occur in air and under water
• Within the same species, there exist geographic differences in sound
characteristics where populations don’t mix.
(c) JASCO Applied Sciences 45 46 (c) JASCO Applied Sciences
• are often described by onomatopoeic words: grunts, snorts, buzzes, sensitivity overlap to some degree with the frequencies of their calls.
barks, yelps, roars, groans, creaks, growls, whinnies, clicks etc. [3; Other indicators for what these animals can hear come from controlled
44] exposure experiments looking for responses of animals to sound.
Emitted Sound Anatomical studies of baleen ears have suggested good hearing
sensitivity between 10Hz and 30kHz. At the low-frequency end, sound
Monodontidae: Beluga & Narwhal
Delphinidae: Dolphins, Killer & Pilot Whales
detection by baleen whales might often be ambient noise limited rather
Phocoenidae: Porpoises than audiogram limited.
Physeteridae & Kogiidae: Sperm Whales
River Dolphins Marine mammal audiograms exhibit a similar U-shape:
Ziphiidae: Beaked Whales • at low f, sensitivity improves as ~ 10dB/octave
Mysticetes: Baleen Whales
Phocids: True, Earless Seals • best sensitivity is between 30 dB re 1µPa (odontocetes) and 70 dB re
Otariids: Fur Seals & Sea Lions 1µPa (pinnipeds), with the exception of the Gervais’ beaked whale
Walrus audiogram, the current estimate of which has a much higher threshold
Sea Otter • at high f, sensitivity drops fast: >100dB/octave
Polar Bear
Monodontidae
Sirenia: Manatee & Dugong
140 Delphinidae
1 2 3 4 5 Phocoenidae
10 10 10 10 10
Lipotidae & Iniidae
Frequency [Hz]
120 Ziphiidae
Figure 35: Frequency bands of marine mammal sounds incl. echolocation Phocidae
[13; 40; 44]. Otariidae
The different types of noise effects can be linked, e.g., a temporary shift
in hearing threshold will affect the audibility of signals (e.g. of
conspecific calls) and thus alter or prevent the ‘normal’ behavioural Figure 40: Population Consequences of Acoustic Disturbance (PCAD)
response to such signals. Or, noise received by a diving animal might model.
induce stress leading to a so-called fight-or-flight response involving
rapid surfacing which can cause decompression sickness and injury, and
ultimately death.