Wednesday, June 27, 2018

No Such Thing As A Term Paper

On this week's No Such Thing As A Fish podcast, Number 222, James's fact at 33 minutes into the recording is this:  “The Gulf Corvina fish has such loud sex that it can deafen dolphins”

I found the article he was referencing, A sound worth saving: acoustic characteristics of a massive fish spawning aggregation, by Brad E. Erisman, Timothy J. Rowell

Here's a tweet with a picture of the Gulf Corvina

At time stamp 41:17 James talks generally about sound underwater, something I have thought about a lot.
James: But I think the problem was that Jacques Cousteau did a documentary, didn't he, in 1956 called The Silent World. It was all about the underwater. But basically his diving tanks masked all the sounds of the water. So he was like, "Oh, it's so quiet in here." And actually that's just where his microphones were. So lots of people thought it was really quiet, but like you say, Anna, it's loud as hell, isn't it?
Anna: "It's not {really quiet} is it? Even though it doesn't work very well with our ears. Because I thought this was really interesting. So sound waves, because they travel a different way in water to how they do in air, and we've got air in our ears, that's why sound is messed up for us underwater, but that's also why whales, you know they have huge amounts of wax in their ears, so you see whale's ear wax, it comes many many inches long ear wax, and that's kind of the same density as water so that means that the sound waves can travel into their ears and they'd be fine. But it's assumed, that if they came up onto the surface they'd be deaf in air."

This is definitely a different way to explain acoustics than anything I encountered in any of my college courses on the subject.

In addition to the Cousteau documentary they mentioned on No Such Thing As A Fish, there was also a book. An autobiography in fact, called The Silent World. I referenced it in a term paper I wrote in graduate school 11 years ago. I can't find the final version of the paper on my hard drive, but I did find these notes that went into it. In keeping with the Quite Interesting tone, here are a collection of facts about underwater hearing and noise and evolution.

Notes for an Oceanography term paper on underwater hearing for FSU around 2007:

Man is an egotistical explorer. Direct observations are limited to the range of the human senses, judgments are based on the human experience. Sensory perception evolved in vertebrates to improve their chances of survival. Because avoiding predators is key to the survival of any individual, hearing developed into the most important warning sense, species by species. Modern human beings can go through their civilized days without needing to know the wavelengths of light they perceive or the frequency of the sound that they hear. While it is common knowledge that dogs have a keener sense of smell than people and can hear high pitched whistles that are silent to our ears, we tend to anthropomorphize our pets and forget our inferiority. It is a bad habit, particularly when making new discoveries. A more modest approach to exploration may reveal an even more complex and beautiful world. This is particularly true when we invade a space where the physics don't match our evolutionary environment. We evolved in the air, not in the water. Here marine mammals have taken a full evolutionary step past us. They experience the world in a way we can only appreciate if we open our minds beyond the limits of our own senses and use our instruments to simulate what they take for granted.

Captain Jacques Cousteau of the French Navy made a great contribution to oceanography with his co-invention of the aqualung and regulator. The physiology of diving was already well researched, particularly by the US Navy, but freeing the diver from his upright posture and hoses to the surface was a breakthrough. Unfortunately the ability to move as freely as the fish, indeed, the ability to freely spear the fish, gave Jacques Cousteau a false impression that he was superior to the creatures of the sea. In his autobiography, "The Silent World," he reveals his strange attitude. "The sea is a most silent world. I say this deliberately on long accumulated evidence and aware that wide publicity has recently been made on the noises of the sea. Hydrophones have recorded clamors that have been sold as phonographic curiosa, but the recordings have been grossly amplified. It is not the reality of the sea as we have known it with naked ears. There are noises under water, very interesting ones that the sea transmits exceptionally well, but a diver does not hear boiler factories." (Cousteau 1953 p. 242)

The hearing loss experienced by human subjects underwater is comparable to those who have an eliminated middle ear, such as because of a radical operation. This constitutes a loss of about 60 dB. (Note that a high quality pair of shooting ear muffs only provides about a 34 dB reduction.) The loss of direction sensation is also expected underwater because of the head and hearing organs being so close to the density of water. Sound localization depends on the two ears working separately. Audiograms made underwater by DeHaan in 1956 and Hamilton in 1957 confirmed the theoretical 60dB hearing loss. In the frequency range of 1000 Hz to 16,000 Hz determination of direction was impossible. Neither the distance between the observer and the source of sound, not the type of sound, namely short pulses or sweep tones, made any difference. (DeHaan 1960).

"The creatures of the sea express fear, pain and joy without audible comment. The old round of life and death passes silently, save among the mammals -- whales and porpoises. The sea is unaffected by man's occasional uproars of dynamite and ships' engines. It is a silent jungle, in which the diver's sounds are keenly heard -- the soft roar of exhalations, the lisp of incoming air and the hoots of a comrade. One's hunting companion may be hundreds of yards away out of sight, but his missed harpoon may be clearly heard clanging on the rocks, and when he returns one may taunt him by holding up a finger for each shot he missed."  (Cousteau 1953 p. 242) Jacques Cousteau wasn't just wrong about sound in the sea, he was kind of a jerk.

Since accepted wisdom is that life originated in the water, it follows that hearing developed there as well. This formation of a sensory apparatus for hearing probably began with the tactile sense, followed by a nervous system, lateral line organ, and finally organs that we think of as the inner ear. Some of the fishes, the most highly developed vertebrates, were able to transition to life on land. Underwater hearing became air hearing, reaching the pinnacle of performance in mammals. (DeHaan, 1960)

Hearing in mammals is the most important source of information on what is happening at a distance. The eye is limited by obstacles that would block a line of sight, where sound would refract around it.  Hearing does not depend on sunlight. Unlike smell it doesn't require the proper wind direction.  The ear gives information first and most rapidly, and is therefore the most efficient warning organ (DeHaan 1960).

Imagine a pool full of children playing Marco Polo. As the other children call out to blindfolded Polo, he flails about to tag them. He is usually dead accurate in guessing which way to turn and how far to jump, the only real challenge being that all the Marcos jump out of the way. This game is an ideal use of the ear for localization. First of all, everybody in the game is calling out at ear level and splashing right on the surface of the pool. Ears on the sides of the head make us really good at localizing sound all around the same plane as our ears, and particularly in front of us where the outer ear reflects sound into the ear canal with maximum efficiency. Our ears do not work nearly as well for localizing sounds in the vertical plane. It's logical to suppose that in our evolutionary past, most of our predators were coming at us from the ground and not attacking from the air. Another reason Polo has an advantage is because the frequency of the human voice falls right in his peak sensitivity to sound. We lose sensitivity at the low and high end of our spectrum, which encompasses 11 octaves, from about 20 Hz to 20,000 Hz.

Although our brain does it automatically without our realizing it, there are two main ways people listening in air can localize sounds, the difference in time of arrival of a sound at the two ears, and the difference in the spectrum of the sound reaching the two ears. Both of these depend on the distance between the ears and the sound shadow of the head and the outer ear.  (Heffner 1980) The spectral difference of the sound involves the phase of the individual frequencies that add together to make the sound wave. This is important at low frequencies where the wavelength is large relative to the size of the head. At about 1500 Hz, the frequency of maximum sensitivity in human hearing in air, the wavelength is just right to make the phase of the waveform the same at both ears. It is very difficult to localize this pitch. Fortunately for Polo, children don't yell in pure tones.

Now imagine all these children put on scuba gear and tried to play Marco Polo. They'd get disgusted and go inside to play video games within ten minutes. They could still holler underwater, but they would barely be able to hear each other. The sound of their bubbles and the kicking and splashing would seem louder than their voices. The one with a blacked out face mask would have no idea if somebody was above him or below him or left or right, if he could hear them at all.

Mammals returned to the water after they evolved to life on land. By considering how their anatomy changed as a result of evolving to marine life, we may better appreciate why human beings are poorly equipped to appreciate the underwater soundscape with the naked ear. All the mammals still have similar inner ears, with a cochlea and basilar membrane described by standing wave physics. It is the pathways to get vibrations into the cochlea that show the most evolutionary difference in the marine mammals and man. The Cetaceans (whales) and Sirenians (manatees and dugongs) are said to share a common ancestor with modern ungulates, the cud-chewing cows and hippopotamuses. The bottlenosed dolphin has a fascinating anatomy for hearing and sound creation, including the ability to mimic sounds it hears, and a sound path to the inner ear through a hollow jaw full of specialized fat. For echolocation, dolphins produce and hear frequencies 3 octaves above the human frequency range, similar to bats. (Verbal, Nowacek) While the dolphins were evolving this predatory advantage, some of their prey were keeping up. While most fish can detect sound to 1-3 kHz, herrings may have evolved to hear echolocation at 180 kHz to avoid predation. (Popper 2000)

Dolphin hearing may be advanced too far beyond humans to make a good comparison. We are only now beginning to decipher the physics of their auditory system. Studying dolphin psychoacoustics could prove even more astonishing. For a simpler anatomy comparison to humans, it would be logical to look at marine mammals that have evolved to live part of their life on land and part underwater.

The evolutionary ancestors of the sea lions and the walruses were small flippered mammals with dense underfur like modern day fur seals. They fed along the coastline, hauling prey onshore to eat. Evolutionary changes in these marine newcomers to accommodate to life in the water included enlarged eyes and circulatory and ear adaptations for prolonged and deep dives. Directional sensitivity to underwater sound was not developed. Sharing a common terrestrial ancestor with bears, the extinct pinnipeds called enaliarctids likely lived all over the coast of the North Pacific until 16 million years ago. (Repenning 1976) As far as hearing underwater goes, we aren't even on an even playing field with an animal that went extinct 16 million years ago. We can't close our ears to the water with special tissues that react uniquely to pressure.

The desmatophocids are a formerly abundant seal that evolved from the enaliarctids, surviving until about 9 million years ago. These creatures were much larger than their ancestor, an advantage in holding heat in cold water, particularly as they adapted to life away from the coast. They are believed to have enjoyed improved directional underwater hearing because the entire ear structure was much more specialized than the enaliarctid ear, with many of the modifications specifically related to isolating the two ears from one another. Acoustical advantages in modern sea lions and walruses, particularly major flat areas on the skull favoring sound reception from selected directions, were missing in this ancestor. (Repenning 1976)

The bony structure and the soft anatomy associated with it has two functions, protection against pressure and sensitivity to sound. The enaliartids had adaptations that indicated it was a deep diver, but few adaptations were for directional sensitivity. 12 million years ago walruses developed directional underwater hearing advantages, and the sea lions 8 million years ago. The walruses are supposed to have undergone a reverse evolution when they changed to a shallow-water bottom feeding lifestyle, losing some of the deep diving protective adaptations, perhaps with improved air hearing as a benefit. (Repenning 1976)

In air, the human outer ear serves to reflect sound waves and direct them into the ear canal, assisting with locational clues, and performing somewhat as an amplifier. The sea lion's ears may serve the same purpose out of the water. In the water, the outer ear loses its function. The density being so similar to water, vibrations pass right through it with no reflection. Furthermore, at low frequencies, underwater sound vibrates the whole skull, including the two hearing organs. In air the middle ears move separately with respect to the inner ear and skull. (DeHaan 1960) This is why it is important that the marine mammals evolved to isolate their inner ears from receiving vibrations from all directions through tissue similar in density to the seawater. Mapping the density of layers of tissues in the heads of marine mammals is a useful technique for modeling acoustic pathways to their inner ear. Studies of this type in manatees recently revealed some previously unknown underwater hearing adaptations. (Verbal, Marie Chapla, 2006)

Even before all these discoveries into the adaptations in hearing anatomy in underwater mammals were made, back in the time of Captain Cousteau's early aqualung diving adventures, scientists were paying attention to the sounds these mammals were making. In a paper in Science, February 1949, William Schevill and Barbara Lawrence of Harvard described sounds of beluga whales heard on underwater listening apparatus. At the time, only the toothed whales were known to make noise at all. The songs of the humpbacks weren't known until later. The listeners, watching the whales with field binoculars, reported  high-pitched resonant whistles and squeals, ticking and clucking sounds, mewing and chirps. Some of the sounds were bell-like, indicating a build up of overtones. Some sounds suggested a crowd of children shouting in the distance. There were sharp reports, and the trilling that gives the beluga the nickname "sea canary".  The author admits it is notoriously difficult to adequately describe unfamiliar sounds. (Schevill 1949) {This study was done in the area of the St. Lawrence Estuary, where these beluga whales are now so contaminated with heavy metals their carcasses have to be treated as hazardous waste. (Verbal, Nowacek 2006)}

Fifty years since this attempt to describe the cetacean sounds, Australian scientists studying fish calls described four sounds fish make -- pop, trumpet, drumming, banging. They suppose several biological reasons for making these sounds: reproductive displays, territorial defense, feeding sounds or echolocation. There is also physical noise -- sea noise, rainfall, breaking surf, seismic noise, low frequency swell, and ice movement (McCauley 2000)

Humans are used to living in a sound field characterized by architectural acoustic concepts such as reverberance and liveness. (Shroeder, 1966) Reflected and diffused sounds make up a large part of our perception of the world around us. Sound reflects off objects underwater exceptionally well, as evidenced by the success of sonar. The 4 to 5 times increase in the speed of sound means that sounds reflected off objects in our range of sight would reach our ears so fast our brain wouldn't perceive it. A psychoacoustic phenomenon known as the precedence effect causes humans to lump all amplitude reduced sounds delayed by up to 35 milliseconds together with the initial sound, even if the second comes from another direction. By 70 milliseconds this breaks down and we begin to recognize an echo. This ability to recognize echos at all is related to separation of sound between the ears -- each ear having a slightly different input. (Wallach 1949) Since one of the primary difficulties man has in hearing underwater is that his whole head vibrates together, that may turn out to be even more important than the delay effect when it comes to detecting reflected sound underwater with the naked ear. "Things seem one-fourth nearer than their actual distance, a deceitful perspective caused by the refraction of light passing from water to air though the glass plate. On my first dive I reached for objects, saw my hand fall short and was dismayed at my shrunken flipper of an arm. ... It takes practice to automatically correct distance and size." (Cousteau, 1950 p.252.) Oddly, there has been no sport diving apparatus developed for the ear. (There's no telling what the Navy has invented for their divers.)

Snapping Shrimp section:

"Syrian fisherman select fishing grounds by putting their heads down into their boats to the focal point of the sound shell that is formed by the hull. When they hear creaking sounds they cast nets. They believe that the sound somehow emanates from rocks below, and rocks mean fish pasturage. Some marine biologists suppose the creaking sound comes from thick thousands of tiny shrimps, scraping pincers in concert. Such a shrimp in a specimen jar will transmit audible snaps. But the Syrians net fish, not shrimps. When we have dived into creaking areas we have never found a single shrimp." (Cousteau 1953, p 243-244)

The Syrians use the hulls of their boats to amplify the noise from the water and compensate for the 99.9 % power loss from water to air. They told Captain Cousteau that they cast their nets because they believe the area has the sort of rocky cover that draws fish, getting right to the point of the matter. Snapping shrimp also like rocks with a lot of hiding places, so it seems to be the most basic A=B, B=C, therefore A=C sort of logic. The fact that Captain Cousteau never found a single shrimp is a testament to the snapping shrimps penchant for hiding. According to Johnson, Everest, and Young's research in 1947, "They are notably secretive and demand ready-made or easily maintained burrows. Hence, they seek concealment in crevices and holes provided by coral, stones, shells, calcareous algae, and other solid objects. It has been demonstrated repeatedly by collectors that they live preponderantly on these bottom types. This habit renders collecting very difficult in most instances, especially when a dredge must be used. Hence the animals are far more abundant than generally realized." It is possible these are the marine biologists Cousteau were referring to, as this research came out before Cousteau's autobiography, although F. Alton Everest, one of the co-authors, was a Physicist at the Naval Ordinance Lab and went on to become the author of the most important acoustic textbook in the US, and is not a marine biologist at all. In Captain Cousteau's defense, the snapping shrimp noise is not as pronounced in the areas where he did the majority of his diving. Mediterranean species Typton spongicola were cited as species capable of snapping that are found in the Mediterranean, but they were not considered numerous in 1947.

Though the extreme level of noise, 30 dB higher than state 1 sea noise*, produced by "thick thousands of tiny shrimps, scraping pincers in concert" has been well known for over half a century, the details of the snap are still coming to light. The noise is not in fact made by scraping pincers at all, but is caused by the popping of a cavitation bubble produced by the rapid movement of the claw. In 2001 researchers at the University of Twente found that the bursting bubble also produced a burst of light. The burst of light is not itself biologically important, being shorter than 10ns and not bright enough to see with the naked eye. It is simply an indicator of the power in the shrimp's snap. The shock wave caused by the bubble collapse is now thought to be capable of stunning prey, not merely scaring away predators. ( (Find article in Nature, OCT 2001) *State 1 sea noise refers to the sound generated by waves that are still growing because of the wind, with crest to trough height of less than 30 cm high.

Lautenschlager 1983
During World War I torpedo boats worked over the battle fleets. It wasn't until after the war that fleet destroyers were equipped with active acoustic detection devices developed first by the Royal Navy as ASDIC and later by the U.S. Navy as Sonar.

Kritzler 1952 Pilot whale at Marineland
High pitched squealing or whistling similar to the three species of dolphins in the tank. Small quantities of air escape as it makes the noise. Used at times of excitement, whether due to fighting, fright, pain, or competition for food. Blow hole smacking noise made in air at times of comparative tranquility when the pilot whale was resting. Third type of noise was a kind of raspberry followed immediately by a breath. Fourth sound was inaudible in air but easily detectable with a hydrophone, reminiscent of a large door slowly swung on rusty hinges. Most noteworthy pilot whale sound was unlike any made by dolphins. Peevish whining of a child, or crying of young porcupines or beavers. Only heard when the whale would elevate its snout higher than normal. Easiest to hear at night when it was quiet, or at any time with the hydrophone.

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