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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 T = period of wave a = amplitude 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 f = 1/T, wavelength λ= c/f T T These waves have the same amplitude but different period, frequency, and wavelength

Pitch (frequency) Larger instruments produce lower frequencies Instrument Range measured in dB Bass drum 35 - 115 Cymbal 40 - 110 Organ 35 - 110 Piano 60 - 100 Trumpet 55 - 95 Violin 42 - 95 Larger instruments produce lower frequencies Instrument dB Bass drum 35-115 Piano 60-100 Trumpet 55-95 Violin 42-95 Voice 40-90

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 Sperm whales form smaller social groups than many toothed whales because their prey (large squid) are more solitary. So they may have to communicate over long distances. Low frequency clicks are for communication, higher frequency clicks (up to 15,000 Hz) for echolocating. Baleen whales do not echolocate. Why not? 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. Frequency f (Hz) Wavelength λ (m) 10 150 100 15 1,000 1.5 10,000 0.15 100,000 0.015 Food too far away OK Minimum echolocation frequency

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 Whales have special adaptations to avoid getting the bends at depth. Bends occur when nitrogen in air in lungs dissolves into blood at increased pressure, then bubbles out in blood when resurfacing. Whales can collapse their lungs during dives to keep air away from lungs so N2 doesn’t dissolve into blood. 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

Blue whales migrate and need to communicate over long distances

High-frequency sounds are absorbed more quickly Absorption 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 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

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 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 Senegal and Madagascar (2008): > 200 pilot whales and melon-head whales

Captive beluga imitates human voice! Humans use acoustics to understand whales. Are the whales doing the same to us? Captive beluga imitates human voice!

A great source of information on sound in the ocean: http://www.dosits.org/