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Announcements

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

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  1. 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)

  2. 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

  3.  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

  4. 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)

  5. Pitch (frequency) Larger instruments produce lower frequencies

  6. 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)

  7. Spectrogram shows how sound spectrum changes over time

  8. 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/

  9. A fish example: Atlantic Croaker Some fish use sound for courting and as a fright response

  10. 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

  11. Baleen (mysticete) whales Toothed (odonticete) whales

  12. 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/

  13. 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.

  14. 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)

  15. Communication frequencies Toothed Baleen Thick bars: most common vocalizations Thin lines: extremes of frequency Mellinger 2007

  16. Echolocation using echoes from sound pulses or clicks Whale can determine distance, angle, size, shape, etc. from sound echoes

  17. Echolocation frequencies Mellinger 2007

  18. 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

  19. 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

  20. 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

  21. Toothed whale foraging:Beaked whales dive deep to find prey Natacha Aguilar de Soto (Yellow indicates echolocation) Peter Tyack et al.

  22. 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

  23. 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

  24. Acoustic receivers used to measure ocean temperature also record whales and other noises Worcester & Spindel 2005

  25. Worcester & Spindel 2005

  26. Blue whales migrate and communicate over long distances

  27. 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.

  28. Transmission loss Sound signal loses intensity due to: -Cylindrical spreading -Spherical spreading -Absorption Blue whale Dolphins

  29. 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

  30. 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

  31. (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

  32. Air-guns disrupt use of sound in foraging Tyack et al. 2009

  33. 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.

  34. 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

  35. 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

  36. Range of effective communication for blue whale singing at 20 Hz and 155 dB Range before mid-1800s Current range (yes, that tiny speck)

  37. 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

  38. 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

  39. 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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