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Use of sound by marine animals
Man-made sounds and their effects on animals
a = amplitude of wave
T = period of wave
f = frequency = 1/T
λ = wavelength (= cT = c/f, where c is sound speed)
a = amplitude
These waves have the same frequency and wavelength but different amplitude
(Amplitude, sound level)
Chart shows loudness in dB of some familiar sounds
Sound levels in air and water have different reference levels, so
0 dB (air) ≈ 26 dB (water)
Frequency = 1/T
These waves have the same amplitude but different frequency and wavelength
Larger instruments produce lower frequencies
Marine animal sounds are made up of multiple frequencies
The sound spectrum gives the pressure level at each frequency
SL [dB] = 10 Log10(I/I0)
SL [dB] = 20 Log10(P/P0)
Worcester & Spindel 2005
Some fish use sound for courting and as a fright response
Snapping shrimp make noise to stun their prey.
They create a cavitation bubble that “snaps” as it collapses.
Toothed (odonticete) whales
Smaller (1.5 to 17 m long)
Most are not migratory
Chase and capture individual fish, squid, crabs
Baleen (mysticete) whales
Larger (15 to 30 m long)
Long annual migrations
Feed on aggregations of krill, copepods, small fish
Social calls - sound for communication
Dolphins live in social groups that stay together 5-10 years. They have “signature whistles” that can be used to recognize individuals at distances of >500 m.
Echolocation using echoes from sound pulses or clicks
Whale can determine distance, angle, size, shape, etc. from sound echoes
Why don’t baleen whales echolocate?
Baleen whales produce low-frequency sounds with long
wavelengths. Wavelength determines the minimum
echo detection distance.
(except for sperm whales)
A cool invention for listening to whales:
acoustic whale tag
Mark Johnson with D-Tag
Natacha Aguilar de Soto
Yellow indicates echolocation
Peter Tyack et al.
Colors: copepod concentration (#/m3)
—: whale trajectory
--: bottom of mixed layer
: Times of visual contacts
: Times of CTD+OPC cast
(OPC = Optical Plankton Counter)
Baumgartner and Mate 2003
Because baleen whales have long, solitary migrations, they need to use low frequencies to stay in communication.
Because toothed whales move in groups, they can use high frequencies without losing communication.
Transmission loss: Sound signal loss of intensity due to cylindrical spreading, spherical spreading, and absorption
Signal-to-noise ratio (SNR)
SNR in decibels indicates how much of the signal can actually be heard over the background noise level.
For communication, need a minimum SNR of 3 to 5 dB.
A good SNR is 20 to 30 dB.
A negative SNR(dB) indicates no signal gets through.
Marine mammal sound levels are generally between 100 and 200 dB
Seals, sea lions, and walruses
Manatees and dugongs
Echolocation (toothed whales)
These add constant background noise
10 to 20,000 Hz
10 to 500 Hz
Up to 232 dB
Low-Frequency Active Sonar
100 to 500 Hz
230 to 240 dB
These are loud enough to damage tissues and cause hearing loss
Since the invention of propeller-driven motors (~150 years ago),
Can use transmission-loss curves to calculate the effective communication range
Blue whale song
20 Hz, ~155 dB
Pre-motor noise level
Whale song stays
above ambient noise
level for ~2,000 km
e.g. San Diego to Seattle
(area ≈10,000,000 km2 )
Current noise level
Whale song stays
above ambient noise
level for ~60 km
e.g. New Brunswick to NYC
(area ≈10,000 km2)
Range of effective communication for blue whale
singing at 20 Hz and 155 dB
(yes, that tiny speck)
Mass strandings associated with Navy sonar activity
The Bahamas (2000):
14 beaked whales, 1 spotted dolphin, 2 minke whales
Bleeding in ears
The Canary Islands (2002):
14 beaked whales
Gas bubbles and bleeding in multiple organs
Mass strandings associated with air guns
Tasmania and New Zealand (2004):
208 whales and dolphins
Senegal and Madagascar (2008):
> 200 pilot whales and melon-head whales
A great source of information on sound in the ocean:
Captive beluga imitates human voice!