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Announcements PowerPoint PPT Presentation


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Announcements. Wednesday: In-class review for exam Yes, today’s material will be on the exam Posted on web: Chemistry review (10/27) Posted on web: Answers to recitation handouts (10/18, 10/27) Today: 1-page paper outline due (turnitin.com) Posted on web: Tips on writing style (11/01).

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Announcements l.jpg

Announcements

  • Wednesday: In-class review for exam

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

  • Posted on web: Chemistry review (10/27)

  • Posted on web: Answers to recitation handouts (10/18, 10/27)

  • Today: 1-page paper outline due (turnitin.com)

  • Posted on web: Tips on writing style (11/01)


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Acoustics and Biology

Acoustics

  • loudness (amplitude or pressure level)

  • pitch (frequency)

    Use of sound by marine animals

  • Predation/defense

  • Communication and social interaction

    Signal-to-noise ratio

    Man-made sounds and their effects on animals


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Same frequency,

Different amplitude

Same amplitude,

Different frequency

Amplitude determines sound level pressure or loudness

Frequency determines “pitch”

Frequency is proportional to inverse of wavelength (f1/)

Waves with different frequencies have different wavelengths


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Loudness

(Amplitude, sound level)

Chart shows loudness in dB of some things we are familiar with

Sound levels in air and water have different reference levels, so

0 dB (air) ≈ 26 dB (water)


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Pitch (frequency)

Larger instruments produce lower frequencies


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Marine animal sounds can be made up of multiple frequencies

The sound spectrum gives the pressure level at each frequency

Intensity  pressure2

dB = 10 Log10(intensity)


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Spectrogram shows how sound spectrum changes over time


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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/


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A fish example: Atlantic Croaker

Some fish use sound for courting and as a fright response


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Toothed whales

Smaller (1.5 to 17 m long)

Social

Most are not migratory

Chase and capture individual fish, squid, crabs

Use sound to echolocate, communicate

Baleen whales

Larger (15 to 30 m long)

Often solitary

Long annual migrations

Feed on aggregations of krill, copepods, small fish

Use sound only to communicate


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Baleen

(mysticete)

whales

Toothed

(odonticete)

whales


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  • Larger whales produce lower-frequency sound

  • Larger whales can dive deeper

  • Toothed whales forage deeper than baleen whales

Data from polaris.nipr.ac.jp/~penguin/penguiness/


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Outgoing sound is generated by the vocal cords and projected through the melon.

Incoming sound is received through the jaw, which transmits sound waves through a fat channel to the ear.


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Social calls

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)


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Communication frequencies

Toothed Baleen

Thick bars: most common vocalizations

Thin lines: extremes of frequency

Mellinger 2007


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Echolocation using echoes from sound pulses or clicks

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


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Echolocation frequencies

Mellinger 2007


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Why don’t baleen whales echolocate?

  • They produce low-frequency sounds with long wavelengths. Wavelength gives the minimum detection distance.

  • Their prey (krill, copepods) are poor acoustic targets

Minimum

echolocation

frequency


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Toothed whale

prey

  • Squid and large fish are:

  • More likely to be solitary

  • Good acoustic targets

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

  • Plankton are:

  • More likely to aggregate

  • Poorer acoustic targets

  • (density similar to water)

Baleen whale

prey


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A cool invention for listening to whales:

acoustic whale tag (D-Tag)

  • Acoustic sensors (hydrophones) and 3D accelerometers in a waterproof, pressure-resistant case, mounted on suction cups

  • Carefully sneak up on whale, attach D-Tag

  • Record audio, pitch, roll, heading and depth

  • Tag pops off, floats to surface 18 hours later

Mark Johnson with D-Tag


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Toothed whale foraging:Beaked whales dive deep to find prey

Natacha Aguilar de Soto

(Yellow indicates echolocation)

Peter Tyack et al.


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

Fig. 4. Eubalaena glacialis and Calanus finmarchicus. (a-d) Examples of diving and tracking observations during feeding behavior. Contoured C. finmarchicus C5 abundance estimated from the OPC casts is shown. Color scale shown in (d) applies to all plots. () Times of visual contacts.

() Times and locations at which a resurfacing occurred and a conductivity-temperature depth/optical plankton counter (CTD/OPC) cast was conducted. Solid and dashed lines indicate the sea floor and the top of the bottom mixed layer, respectively, measured at the location of each CTD/OPC cast.

Baumgartner and Mate 2003


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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


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Acoustic receivers used to measure ocean temperature

also record whales and other noises

Worcester & Spindel 2005


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Worcester & Spindel 2005


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Blue whales migrate and communicate over long distances


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

Because baleen whales have long 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.


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Transmission loss

Sound signal loses intensity due to:

-Cylindrical spreading

-Spherical spreading

-Absorption

Blue

whale

Dolphins


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Man-made noise in the ocean

These add constant background noise

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


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Humans add noise to the ocean

Potential effects of man-made sounds on marine mammals:

  • Temporary or permanent hearing loss or impairment

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

  • Death from lung hemorrhage or other tissue trauma

  • Psychological and physiological stress


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(Bold, filled diamonds, mean of all six singers; other symbols, individual singers). The maximum received level of the sonar at the whale ranged from 130 to 150 dB re 1 Pa. Songs were grouped in the exposure condition if a sonar transmission occurred at any point during the song. The average number of songs per singer in the pre-exposure, exposure and post-exposure conditions was 3.2, 4.7 and 3.8, respectively. Differences were assessed using a mixed-model analysis of variance treating exposure condition as a fixed factor, whale identity as a random factor, and each song duration as an independent observation. The effect of exposure condition on song duration was statistically significant at P=0.047 (F2,10=4.200, power=0.50, n=6).

Miller et al. 2000

Humpback whale songs are several minutes longer in the

presence of low-frequency active sonar


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Air-guns disrupt use of sound in foraging

Tyack et al. 2009


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Signal-to-noise ratio (SNR)

Isignal = power of communication signal

Inoise = power of background noise

(intensity is proportional to pressure squared)

For communication, need a minimum SNR of 3 to 5 dB.

A good SNR is 20 to 30 dB.


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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


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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


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Range of effective communication for blue whale

singing at 20 Hz and 155 dB

Range before

mid-1800s

Current range

(yes, that tiny speck)


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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

Senegal and Madagascar (2008):

> 200 pilot whales and melon-head whales


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Toothed whales

Smaller (1.5 to 17 m long)

Social

Most are not migratory

Chase and capture individual fish, squid, crabs

Use sound to echolocate, communicate

Baleen whales

Larger (15 to 30 m long)

Solitary

Long annual migrations

Feed on aggregations of krill, copepods, small fish

Use sound only to communicate


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A great source of information on sound in the ocean:

http://www.dosits.org/

Oceanus has many articles on sound in the ocean:

http://www.whoi.edu/oceanus/viewTopic.do?o=read&id=83&type=11


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