L4 : Human noise in the Sea

Question 1

why is sound important in the sea

Answer 1

sound travel 5x faster underwater
- light penetrates only shallow depths
thus sound being main sense for marine organisms

Question 2

sound basics

Answer 2

• pressure wave
• measured in frequency (long wavelength = low freq.)
• lower frequencies travel much further than high frequencies

Question 3

sound propagation in the sea

Answer 3

speed of sound increases with the increasing water temp, increasing salinity and increasing density

Question 4

Deep sound channel

Answer 4

• sound waves in this layer get ‘trapped’ between water layers
• near bermuda, at 1000m
• shallower in temperate waters
• beyond about 60 N or S it reaches the surface
• sound can travel over 1000km

Question 5

natural noise

Answer 5

• earthquakes
• ice
• turbulance
• breaking waves
• rain
• bubbles and spray
• marine life…

Question 6

shipping
[anthropgenic noise]

Answer 6

• propeller cavitation, flow noise, engine noise
• contributes noise 95-500 Hz (low freq)
• increased low freq. noise to the ocean at a rate of 3d.b per decade (doubling every decade)

Question 7

Seismic Surveys
[anthropgenic noise]

Answer 7

• airgun : sends high energy sound into the seabed to find oil, determine seabed etc
• sound concentrated <300 Hz but energy spills into higher frequencies (up to 15 kHz recorded)

Question 8

Naval Sonar
[anthropgenic noise]

Answer 8

• use high energy mid/low freq. sonar to find subs
• low freq (LFA) = 100-500 Hz
• mid freq. (MFA) = 2-8 kHz
  linked to whale strading and the bends

Question 9

Construction
[anthropgenic noise]

Answer 9

• detonations
• pile driving
  a. offshore wind farm construction
  b. very loud noise
  c. 100 Hz - 10 kHz
• temp. displacement of marine mammals

Question 10

fisheries
[anthropgenic noise]

Answer 10

• sonar to find fish
• acoustic deterrents/pingers to scare marine mammals from nets

Question 11

Science
[anthropgenic noise]

Answer 11

• side scan sonar
• fisheries sonar
• ADCP (high freq. sound to measure ocean currents)
• depth sounders
• ATOC
• play back experiments

Question 12

ADCP

Answer 12

acoustic doppler current profiler

Question 13

ATOC

Answer 13

acoustic thermometry of the oceans climate

Question 14

Noise Legislation

Answer 14

• noise classed as pollution under MSFD
• guidelines on shipping noise under IMO
• many species protected under various laws prohibiting harm or injury to protected species
• monitoring & mitigation often required under EIAs

Question 15

IMO

Answer 15

international maritime organisation

Question 16

EIAs

Answer 16

environmental impact assessments

Question 17

UK noise monitoring networks

Answer 17

monitor baseline levels of noise
- determine good environmental status for noise pollution
- now includes Bangor and Plymouth

Question 18

GES

Answer 18

good environmental status

Question 19

Marine organisms and sound

Answer 19

most marine mammals use sound
- mammals have widest range of hearing
- seabirds and fishes also have good hearing in lower range (<4kHz)
- Human noise overlaps all species sounds from fish to marine mammals

Question 20

Cormorants sound

Answer 20

(bird)
- can hear sounds underwater between 1-4 kHz
the same freq. their prey - sculpin and herring vocalise at

Question 21

invertebrates sound

Answer 21

oysters can ‘hear’ the sounds of the sea
close at sounds between 10 Hz - 1 kHz

Question 22

TTS

Answer 22

-temporary threshold shift

Question 23

PTS

Answer 23

permanent threshold shift

Question 24

hearing

Answer 24

• most known about odontocetes (toothed whales)
• high freq. limit
• maximum sensitivity
• odontocetes sensitive to higher freq.
• sensitivity overlaps vocalisation range

Question 25

difficulties measuring hearing sensitivity

Answer 25

• requires captive animals
  limits species you can study
• cant stimulate depth

Question 26

Death by noise

Answer 26

• > 100 melon-headed whales died in 2008 NW Madagascar
  now linked to 12 kHz side-scan sonar for mapping of sea bed
  used by oil/gas research

Question 27

PTS / TTS : pile driving noise

Answer 27

PTS within 5m (cetaceans) and 20m (pinniped)
TTS within 10m (cetaceans) and 40m (pinniped)

Question 28

Increased stress / change in fitness

Answer 28

• evidence for increased stress in right-whales from shipping traffic
• noise reduced growth and reproduction rates brown shrimp
• increased fish metabolic rate and predation with noise

Question 29

change in behaviour

Answer 29

• displacement (move away from sound)
• change in movement
• change in vocalisations
• change in surfacing patterns
  (- fitness consequences )

Question 30

grey seal pups and shipping noise
[case study]

Answer 30

1. propagation models built
2. feed model with true ship location (from AIS)
3. overlay seal locations and dives - what noise do they hear?

Question 31

AIS

Answer 31

automatic identification system

Question 32

masking

Answer 32

• when noise interferes with organisms ability to hear
• masking navigation sounds (e.g evidence that reef fish find their reef from its sound)

Question 33

PCOD

Answer 33

population consequences of disturbance

Question 34

mitigation

Answer 34

• ‘ramp-up’ of sound levels
• MMOs on naval and seismic vessels (stop when animal seen/heard)
• acoustic deterrents
• avoidance to critical times/locations to animals
• monitoring

Question 35

MMOs

Answer 35

marine mammal observers