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Test audio/video. Announcements. Yes, today ’ s material will be on the exam Monday: In-class review for exam Email us if you need the paper deadline extended until noon Dec. 13. Please remember to do course evaluations for all instructors at https://sakai.rutgers.edu. Acoustics and Biology.

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#### Presentation Transcript

• Test audio/video

### Announcements

• Yes, today’s material will be on the exam

• Monday: In-class review for exam

• Email us if you need the paper deadline extended until noon Dec. 13.

• Please remember to do course evaluations for all instructors at https://sakai.rutgers.edu

### Acoustics and Biology

Acoustics

• loudness (intensity) and pitch (frequency)

• How to read a spectrogram

Use of sound by marine animals

• Predation and defense

• Echolocation

• Communication and social interaction

Signal-to-noise ratio

Man-made sounds and their effects on animals

### Anatomy of a sound wave

a

T

a = amplitude of wave

T = period of wave

f = frequency = 1/T

λ = wavelength (= cT = c/f, where c is sound speed)

### Amplitude determines sound level pressure, this determines loudness

a = amplitude

a

a

These waves have the same frequency and wavelength but different amplitude

Loudness

(Amplitude, sound level)

SL(dB)=20 log10(P/Pref)

SL(dB)=10 log10(I/Iref)

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 determines “pitch”

Frequency = 1/T

T

T

These waves have the same amplitude but different frequency and wavelength

Pitch (frequency)

Larger instruments produce lower frequencies

Instrument dB

Bass drum35-115

Piano 60-100

Trumpet55-95

Violin42-95

Voice40-90

Marine animal sounds are made up of multiple frequencies

The sound spectrum gives the pressure level at each frequency

Intensity pressure2

SL [dB] = 10 Log10(I/I0)

SL [dB] = 20 Log10(P/P0)

### Spectrogram shows how sound spectrum changes over time

Worcester & Spindel 2005

### A fish example of sound use: Atlantic Croaker

Some fish use sound for courting and as a fright response

### An invertebrate example: snapping shrimp

claw crab

Snapping shrimp make noise to stun their prey.

They create a cavitation bubble that “snaps” as it collapses.

http://stilton.tnw.utwente.nl/shrimp/

Toothed (odonticete) whales

Smaller (1.5 to 17 m long)

Social

Most are not migratory

Chase and capture individual fish, squid, crabs

Echolocate, communicate

Baleen (mysticete) whales

Larger (15 to 30 m long)

Often solitary

Long annual migrations

Feed on aggregations of krill, copepods, small fish

Communicate long-distance

Baleen

(mysticete)

whales

Toothed

(odonticete)

whales

Baleen whales

Toothed whales

 Toothed whales

 Baleen whales

Social calls - sound for communication

Frequency (Hz)

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.

Time (s)

Echolocation using echoes from sound pulses or clicks

Whale can determine distance, angle, size, shape, etc. from sound echoes

Echolocation frequencies

Toothed whales

Why don’t baleen whales echolocate?

Mellinger 2007

### 1. They don’t produce high enough frequencies

Baleen whales produce low-frequency sounds with long

wavelengths. Wavelength determines the minimum

echo detection distance.

Minimum

echolocation

frequency

(except for sperm whales)

### 2. Baleen whale prey (krill, copepods) are poor acoustic targets

• Toothed whale prey:

• Squid and large fish

• More likely to be solitary

• Good acoustic targets

• (squid pens and fish swim bladders have density different from water)

• Baleen whale prey:

• Plankton and small fish

• More likely to aggregate

• Poorer acoustic targets

• (density similar to water)

Toothed whale

prey

Baleen whale

prey

A cool invention for listening to whales:

acoustic whale tag

• Hydrophones and 3D accelerometers in a waterproof, pressure-resistant case with suction cups

• Sneak up on whale, attach D-Tag

• Record audio, pitch, roll, heading, depth

• Tag pops off, floats to surface 18 h later

Mark Johnson with D-Tag

### Toothed whale foraging:Beaked whales dive deep to find prey

Natacha Aguilar de Soto

Yellow indicates echolocation

Peter Tyack et al.

### Baleen whale foraging: Right whales dive to bottom of the mixed layer where plankton are most concentrated

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

### High-frequency sounds are absorbed more quicklyAbsorption of sound in SOFAR channel

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

Blue

whale

Dolphins

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

Baleen whales

Toothed whales

Seals, sea lions, and walruses

Manatees and dugongs

Echolocation (toothed whales)

earthquake

rainfall

### Man-made noise in the ocean

Outboard engine

6,300 Hz

Commercial Ship

10 to 20,000 Hz

Airgun

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),

• Background noise level in the ocean has increased by ~45 dB

• Lowest background noise f has dropped from ~100 Hz to ~7 Hz

After motors

~7 Hz

Before motors

~100 Hz

After motors

~75 dB

Before motors

~30 dB

Can use transmission-loss curves to calculate the effective communication range

Blue whale song

20 Hz, ~155 dB

Pre-motor noise level

30 dB

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

75 dB

Whale song stays

above ambient noise

level for ~60 km

e.g. New Brunswick to NYC

(area ≈10,000 km2)

Blue

whale

Range of effective communication for blue whale

singing at 20 Hz and 155 dB

Range before

mid-1800s

Current range

(yes, that tiny speck)

### Potential effects of man-made sounds on marine mammals

• Disruption of feeding, breeding, nursing, acoustic communication and sensing

• Psychological and physiological stress

• Temporary or permanent hearing loss or impairment

• Death from lung hemorrhage or other tissue trauma

### Noise-induced mass strandings

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

> 200 pilot whales and melon-head whales

A great source of information on sound in the ocean:

http://www.dosits.org/

### Humans use acoustics to understand whales. Are the whales doing the same to us?

Captive beluga imitates human voice!