1. Underwater noise from maritime sources and impact on marine life
Cato C. ten Hallers-Tjabbes

2. Perceiving stimuli (signals) from the environment is vital
for animal behaviour
In a marine environment vision is limited
Acoustic sense and chemoreception instead
Vision can perceive many signals together in a space
(overview)
Acoustic sense can perceive one signal at a time;
the stronger one is heard

3. Acoustic signals from the environment for animal behaviour and communication
Sounds generated in the physical environment:
Sounds from conspecifics:
Sounds from other species:
Predator/prey
Symbionths
Echolocation: self-generated signals
Navigation / orientation

4. Human activities that generate sound
Shipping
Fisheries
Benthic trawling
Sonar
Mineral extraction
Military activities
Shooting / explosions
Dredging
Construction work
Sequestration of carbon dioxide

5. Impact of man-made sound on marine life
Temporary or permanent threshold shift = Deafening
Damage to hearing and other vital organs:
Excess sound disturbs the natural diving pattern.
Lethal if severe
Avoidance of favourable areas for
Feeding, Reproduction, Shelter, a.o.
Inhibition of sensory-mediated
behaviour

6. How do marine animals detect sound
The level of background noise influences the potential of detection
Verboom, 2006

7. Man-made noise may affect animal acoustic perception when:
The frequency range of man-made noise overlaps with the animal’s acoustic perception window
and
Man-made noise is louder than the sounds animals are naturally perceiving
The acoustic window to
the outside world also
offers an opportunity
to enter [or intrude]
Verboom, 2006

8. Examples of fish and marine mammal audiograms
Porpoise = guideline Verboom
Seal = guideline Verboom
Cod = Chapman & Hawkins (1973), Hawkins (1993)
Herring = estimate Enger (1967)
< resulting auditory
filters
Porpoise and seal audiograms = based on several measurements (combination of results).
Cod = measured audiogram.
Herring = estimated, based on evoked potential measurement.
Hearing filter = reversed shape of the audiogram
Verboom, 2006

9. Man-made sound and animal acoustic perception Weighted levels of pile driving noise
Each species hears a different spectrum of the same sound.
Crosses = Broadband peak level of one hit during pile driving.
The red part of the spectrum is the spectrum a herring hears; level = 237 dB (assuming the audiogram of picture 2).
The green part is the spectrum a porpoise hears; level = 207 dB.
So, the herring hears the low-frequency part, the porpoise the high-frequency part.
Pile driving has more influence on herring and cod than on porpoise.
A weighted level is the level of a certain sound spectrum filtered by the hearing filter of a certain species.
Verboom, 2006
Red = Herring hearing spectrum Green = Porpoise hearing spectrum

10. Animal perception of human-generated sound levels calculated weighted source levels
Broadband (free-field) source level and weighted levels per species (dB re 1 microPa at 1 m)
broadband
cod
h. seal
porpoise
herring
wind turbine pile driving
256
228
225
207
237
Airgun – seismic exploration
220
184
161
224
LFAS – military sonar
218
213
185
shipping noise upper limit
199
193
179
173
197
wind turbine in operation
162
148
135
176
shipping noise lower limit
160
144
138
122

11. man-made sound sources and marine animal acoustic windows
Verboom, 2006
Free-field source level of some man-made underwater noises.
Broadband levels are indicated in the legend. Free-field = level of which the influence of local conditions (i.e. bottom and water surface effect on propagation) is eliminated. Upper and lower limit of shipping noise = spreading of 25 ships, length between m, speed between 8-16 knots, noise reduction measures on board = between ‘none’ and ‘pretty good’. Pile driving level is the peak level of one hit. Airgun is the level of one small airgun.
Hearing range = frequency range between max sensitivity (0 dB) and minus 15 dB of the relevant audiogram. Dotted line = no audiogram available.

12. Dose-response relationship Porpoises
Verboom, 2006
Dose-response relationship is the relationship between a certain sound level and a certain effect on the behaviour of an animal. For habour porpoises this relationship has been estimated by TNO, partly based on Dutch research results (Seamarco). It was found that the ‘discomfort threshold’ for certain sound types was around 105 dB re 1 micropascal. The discomfort threshold is the level that an animal usually does not exceed when approaching a sound source.
Shipping sound is between 122 and 173 dB at 1m distance from the ship (weighted free-field source level).
When an approaching porpoise does not exceed a weighted level of 105 dB, the porpoise stays between 560 m (upper limit) and 0 m (lower limit) away from the ship.
Radius of Shipping Noise for Porpoises is ~0 – 560 m, based on a Discomfort Threshold of 105 dB

13. Avoidance of man-made sound hampered in crowded shipping areas
Netherlands Government, 1995
Shipping density
= 45 Ships/Day

14. Migratory Routes Fish and invertebrates Migrate too Few migratory
(Shirihai &
Jarett, 2006.
Whales,
Dolphins
and Seals)
Few migratory
routes
are known
Grey Whale
Killer Whale
Fish and
invertebrates
Migrate too
Global shipping densities as reported
to AMVER (Source: AMVER 2002)

15. Frequencies and Sound Levels
Evaluating the impact of man-made sound on marine life:
Frequencies and Sound Levels
Hearing properties
Masking of pure tone
Irregular sound
propagation
- Frequency ->

16. Conclusions
Shipping and other man-made sound sources in the ocean are likely to increase
Shipping routes coincide with migratory routes of marine animals
The role of acoustic impact on ecosystem functioning may be much larger than currently understood
Sound levels of ships may be higher than necessary due to imperfectly moving mechanical parts,
Improving mechanical performance reduces excess sound levels and reduces operational costs
IMO may be the appropriate International Organisation to take a lead in developing a strategy to reduce the impact of man-made sound in the marine environment