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25 December 2014

NAVIGATION FAILURE IN MASS STRANDED WHALES

Watch this short National Geographic video:


The announcer closes by asking: "What might have disoriented them?"

The is the same question the Deafwhale Society set out to answer 42 years ago. We were as convinced then as we are now that we must first understand why they beached themselves before we can prevent the ultimate collapse of the species. It took us a long time We now understand the cause of stranding. Our current mission now is to educate the public and then start working on ways to truly save these magnificent animals for future generations.

Pods of whales and dolphins mass strand because they are suffering from echo-navigation failure due to barotrauma in their cranial air spaces.

As every scuba diver knows, rapid/excessive changes in the surrounding (ambient) water pressure during a dive will injure the sinus membranes and may damage the middle ear air cavities. The same would happen in an airplane flying above 30,000 feet if cabin pressure was suddenly lost. In fact, any sudden change in ambient pressure that exceeds our ability to counterbalance can cause internal sinus injuries and pain.

Rapid up and down pressure flucuations are especially dangerous for all air-breathing diving mammals because the air in the enclosed air spaces both compress and expand during exposure, while bodily tissues, blood, and bones do not. During these changes in air volumes, strong pressure differentials develop at air-filled interfaces causing shear forces that tear, bruise, and disrupt tissues, membranes, and blood vessels.

This type of injury is called barotrauma.  It happens because the volume of air inside the cranial air spaces fluctuates in lockstep with any pressure change. Barotrauma is the most common injury in scuba diving and is likely the most common injury in whales.

Rest assured, rapid and excessive changes in water pressure is and divers worst nightnmare come true. Toothed whales and dolphins are no excepttion. These diving mammals have massive head sinuses. In fact, excluding bone and brain tissue, roughly 30% of the total volume of the head of a diving pilot whale is made up of volumes of air enclosed in various sinuses, air sacs, and middle-ear air chambers. Calling a pilot whale an airhead is technically correct.

What most whale-loving folks dont know is that the massive air sinuses in deep diving whales and dolphins serve underwater as acoustic reflectors (mirrors), playing a major role in the workings of their echo-navigation and echo-location system. Toothed whales and dolphins also have a special grouping of air sacs situated in the space between their two cochleas. These pockets of air serve to isolate the left and right organs of hearing from each other in the same fashion as a pair of stereo headphones isolate the sounds entering the left and right ears of humans. If diving whales lose the ability to hear stereoscopically, they lose their sense of direction.

Barotrauma in the cranial air spaces of toothed whales or dolphins would not only disable their echo-navigation, but also prevent them from echo-locating their prey.

Imagine for a second that a pod of pelagic dolphins are on a deep feeding dive when a natural undersea catostrophic event suddenly errupts below them. If the seafloor dances in the vertical plane, the up and down jerking would push and pull at the bottom of the water column causing rapid and excessive changes in diving pressures. This means that an entire pod might suffer barotrauma all at the same time.

When the injured pod surfaced, they would be as lost as a blind man thrown overboard in the middle of the deepest ocean.

Seaquakes rock big oceangoing trawlers and easily wipe out oil tankers so you can safely bet that these events can also injure pods of diving dolphins and whales.


THE EVIDENCE

Professors Kenneth Norris and George Harvey first suggested that healthy cranial air spaces were necessary for echo-navigation in their 1972 paper entitled "A Theory for the Function of the Spermaceti Organ of the Sperm Whale." (Link to this highly recommended article) Therein, these two famous cetologists state:
"The structure of the two vertically oriented air sacs that bound the ends of the spermaceti organ suggest that they are sound mirrors. The posterior sac (the frontal sac) possesses a knob-covered posterior wall that is probably an adaptation allowing maintenance of the sound mirror in any body orientation and during deep dives, Finally this complex anatomical system is suggested as a device for the production of long range echolocation sounds useful to the sperm whale in its deep sea habitat, in which food must be located at considerable distances in open water." 
Moreover, on page 20 (chapter 16) of a 1977 book, edited by Professor Norris entitled Whales, Dolphins, and Porpoises, the famous cetacean anatomists and curator at the British Museum of Natural History, Dr. Peter Purves,  stated:
 "It is very easy to imagine a condition in which the air-sac system has broken down, so that it is no longer reflecting, and, with the isolation of the essential organs of hearing disrupted, the animal may loose it's sense of direction." 
Deafwhale Society's seaquake theory is in total agreement with what Prefessors Norris, Harvey, and Purves said 40 years ago. Seaquake-induced barotrauma would indeed cause the breakdown of the air sac system, which would result in the whales loosing all sense of direction. In fact, reading Dr. Purves' comments was what led us to reseach barotrauma as a cause of mass strandings. 

The acoustic purpose of the sinuses was recently confirmed by Drs. Alex Costidis and Sentiel A. Rommel (Link) who wrote:
"The cetacean accessory sinus system is unique; these un-pigmented mucosa-lined structures, which are located on the ventral aspect of the skull, are typically associated with hearing and acoustic isolation of the ears. The ventral sinus system is distinguished from the dorsal air sacs by appearance and function; the lining of the dorsal sacs is composed of pigmented epithelium and these sacs are associated with sound production."
For those readers who would like to dig deeper into the connection between cranial air spaces and echo-navigation, I highly recommend "Anatomic Geometry of Sound Transmission and Reception in Cuvier’s Beaked Whale (Ziphius cavirostris)" by Ted Cranford et al. (Link)


Ted's drawing above depicts the back view of the air chambers (aka: acoustic mirrors) in the head of an adult beaked whale. The back third of the lower jaw, known as the pan bone, is very thin (white). Its internal fat (MFB) fills the hollow region within the lower jaw and terminates near the ear complexes (TPC). The air-filled maxillary and peribullary sinuses (blue) are large and also form acoustic shields (mirrors) to isolate the two ears from one another. (Link)

STEREO RECEPTION DURING DEEP DIVES

As pressure builds during a dive, a scuba diver's regulator furnishes compressed air to keep the sinuses at their normal surface volume thereby preventing sinus squeeze. Even though whales have no scuba tanks, the air in their cranial air pockets still maintains surface volume even on a deep dive. This is so because, after 50 million years of diving, evolution has arranged it so that, as the volume of air is reduced in the air chambers of the head by the increasing ambient pressure during a dive, the whale can shift compressed air from its lungs into the sinuses to keep them properly inflated and ensure that its biosonar continues to function at depth. Shifting the air from the lungs does not cause a lung squeeze because the ribs are hinged allowing the lungs to collapse almost flat. In this fashion, deep divers have lots of air to fill the sinuses and keep their biosonar system working down to their maximum diving depths -- reached when all the available air in their lungs is shifted to the cranial air spaces.

RAPID AND EXCESSIVE CHANGES IN DIVING PRESSURES DURING A DIVE

This system of enclosed air spaces is an evolutionary marvel; however, there is an inherent danger to diving to great depths with a head full of compressed air. The tissues, ligaments, and membranes surrounding, attached to, or near these air cavities are susceptible to injury when a sudden oscillation in the ambient water pressure causes the volume of the air to fluctuate so rapidly and excessively that it cannot be rendered harmless by the whale's pressure-regulating anatomy.

Whales have wads of blood vessels that lay flatened, taking un very little space. When the pressure suddenly drops and the sinus air compresses to occupy a small space, these bllod vessels engourge themselves to occupy the space and prevent sinus squezze. However, their are times with this protection can not counter disturbances of great and rapid pressure vascillations extended in time.

This evolved protection can be overcome by over and under pressures generated during undersea earthquakes, explosive volcanic eruptions, the violent impact of a heavenly body with the water's surface, underwater explosions, exposure to military sonar, and to oil industry airguns. All these vibrational sources generate waves of sudden changes in diving pressures that are EXTREMELY hazardous to all divers who venture below the surface with enclosed pockets of air. The list of animals that might beinjured includes whales, dolphins, manatees, seals, walruses, penguins, polar bears, fish with swim bladders, sea otters, sea turtles, and human divers.

preparing to refloat a beach pilot whale

Imagine a pod of pelagic toothed whales or dolphins (odontocete) feeding on squid above the mid-oceanic ridge system when a violent mid-size earthquake suddenly erupts below them. Not much happens if the seafloor moves from side to side (horizontal) because water will not transfer shearing motion. It's like turning your boat paddle sideways. On the other hand, if the seabed dances vertically, the rapid up and down piston-like motion of the rocky bottom pushes and pulls at the water column, generating powerful low frequency (LF) changes in hydrostatic pressure that travel towards the surface at 1,500 meters per second.

WHALE-DANGEROUS UNDERSEA EARTHQUAKES

Most whale scientists known nothing about earthquakes in the seafloor. They think that quakes of similar magnitude should be equally dangerous, but that's not true. The intensity of any changes in pressure is not as much related to the magnitude as it is to the peak ground acceleration of the shifting seabed and the depth of the EQ's focal point below the rock/water interface. 

The faster the seafloor dances up and down, the greater the pressure changes in the water. A similar increase in pressure happens when the focal point of the rupture is only a few kilometers below the seafloor. During events focused less than 5 km deep, the seismic shock waves reach the rock/water interface long before the energy spreads out and weakens.

In simple terms, the dancing seafloor becomes like the faceplate of a gigantic sonar transducer ~10 miles in diameter. As an extreme example, NASA physicists estimated the shock wave of a 7.5 earthquake at 90,000 pounds per square inch (psi) one meter off the seafloor (Link). This level of vacillating pressure would drop drastically as the shocks fan out in the water above.

We know that healthy toothed whales and dolphins use sound to find their way around in the open sea. They produce loud clicks by moving air back and forth within their elaborate nasal air sac system. The echoes that bounce back from the seafloor are received by the lower jaw in a modified form of bone-conduction. From the jaw, these vibrations are transferred into a fat filled channel and then carried in acoustic fat to the cochlea (inner ear). The brain then compares the sonogram of the echoes with memory. They know where they are because they been there before.



The intensity of the echoes entering the fat filled channel depends on the angle of the lower jaw to the source. In the simplest terms, all a toothed whale needs to do to read the returning echo is to pan her head back and forth until she extracts all the vital data she needs to pin point her location.

Since the outbound clicks are focused via the oil-filled melon by bouncing sound off the skull, there must be a mechanism to isolate the two cochlea from the skull otherwise the volume of the outgoing clicks would overwhelm the returning echoes. This acoustic isolation of the inner ears is accomplished by surrounding them with a mixture of air and foam contained in a grouping of air sacs called the pterygoid sinuses. The middle ear also has a set of enclosed air spaces that aide echo-navigation. Air works as the perfect sound barrier underwater because the acoustic impedance mismatch between air and water causes waterbourne clicks to be reflected in a similar fashion to how light is reflected from a mirror.

To drive home the point... air serves not only for acoustic isolation, but also to reflect sound in the proper direction to insure the function of their navigation system. Let something go wrong with the sinuses and air sacs and the whales can no longer navigate. Nor can they dive and echo-locate their prey. They become lost at sea and unable to feed themselves. Since their fresh water comes from the food they eat, they will soon become dehydrated.

The degree of injury in the internal sinuses, and middle-ear air cavities will depend on the percentage of change in the surrounding water pressure coupled with the duration and frequency of infrasonic waves. The closer the whales are to the surface, the more danger they face because the percentage of change is greater in shallow water. As an example, imagine a pod of diving whales are suddenly exposed to potent oscillating changes in ambient water pressure at ~10 cycles per second while only 10 meters below the surface where the absolute pressure is ~30 pounds per square inch (psi). Suppose, at the same depth as the whale, a seaquake has induced absolute pressure changes oscillating between ~300 psi above ambient followed by a negative ~300 psi below ambient. The air in their enclosed air spaces will suddenly compress to 1/10th of its normal volume on the positive pressure phase and then expand a microsecond later to 10 times normal volume on the negative pressure phase (1,000% change).

Woods Hole Oceanographic Institution (link) exposed a dead dolphin to shock waves measured at ~300 psi. Dr. Darlene Ketten reported (OCEAN MAGAZINE Vol. 47, page 2, 2009):

“Dolphin carcasses can suffer essentially no significant damage in the received range of 10 to 15 psi and significant damage to some organs above 25 psi. At 300 psi, dolphins, well, basically, are mush. For comparison, 20 psi is about the pressure a 200-lb. man's shoe heel exerts on a floor when he walks, and a large dog's jaws can produce 400 psi of pressure when it bites."
The above results would not be the same in a living dolphin for three important reasons: (a) the sinuses and air sacs collapse on death, (b) live dolphins have anatomical means of dealing with sudden pressure changes, and (c) a shock wave from an explosive source has a much faster rise time to peak pressure and would naturally do far greater damage than a 300 psi pulse from an undersea earthquake. On the contrary, the cycle of compressions/expansions in the volume of air in the heads of living whales would continue, on average, 10 times every second until the seaquake ended, or until the whales reached the surface and raised their heads out of the water. Diving whales might be exposed to 20 seconds of continuing pressure changes during an average undersea quake.

It could be that when the sinus membranes tear, air mixed with loose blood escapes into the head forcing the sinuses to close. The membrane might heal in a week or so, but how long would it take the whale to absorb the loose air and blood from his head? The injury might also be in the accessory air sinuses of the middle ear, or in many different places within the extensive system of the sinuses and air sacs. It might even be in the nerves. No matter where the injury, the resulting barotrauma will destroy their ability to echo-navigate, and prevent them from diving and feeding themselves. Their recovery would be slow. One day they might be able to dive to 20 meters. They might reach 50 meters a few days later. Best guess is that the recuperation process might take from 7 to 30 days depending on the original injury and on whether the injured pod is able to catch an occasional meal.

Recovery would have naturally been much easier a hundred years ago because there was far more food near the surface for them to eat. Recovery today is likely to be 2-3 times more difficult, which offers an answer for why more pods are stranding today then in the past.

None-feeding whales would become dehydrated because all their fresh water comes from the food they eat. Besides the loss of their sense of direction and the loss of their ability to dive and feed themselves, their other problems would be shark attack, malnutrition, weakened immune response, and severe stress. Other than an attack by sharks, being washed onto a sandy beach by a strong shoreward current would be the second worse possible outcome for the lost whales.


Scientific Articles Supporting the Above Conclusions:

Aroyan, J. L. (2001). “Three-dimensional modeling of hearing in Delphinus delphis,” J. Acoust. Soc. Am. 110 (6), 3305–3318.

Aroyan, J. L., Cranford, T. W., Kent, J., and Norris, K. S. (1992). “Computer Modeling of Acoustic Beam Formation In Delphinus delphis,” J. Acoust. Soc. Am. 92 (5), 2539–2545.

Balcomb, K. C. III and Claridge, D. E. (2003). “A mass stranding of cetaceans caused by naval sonar in the Bahamas,” Bahamas J. Sci. 2, 2–12.

Brill, R. L., and Harder, P. J. (1991). “The effects of attenuating returning echolocation signals at the lower jaw of a dolphin Tursiops truncatus,” J. Acoust. Soc. Am. 89, 2851–2857.

Cox, T. M., Ragen, T. J., Read, A. J., Vos, E., Baird, R. W., Balcomb, K., Barlow, J., Caldwell, J., Cranford, T., Crum, L., D’Amico, A., D’Spain, G., Fern├índez, A., Finneran, J., Gentry, R., Gerth, W., Gulland, F., Hildebrand, J., Houser, D., Hullar, T., Jepson, P. D., Ketten, D., MacLeod, C, D., Miller, P., Moore, S., Mountain, D., Palka, D., Ponganis, P., Rommel, S., Rowles, T., Taylor, B., Tyack, P., Wartzok, D., Gisiner, R., Mead, J., and Benner, L. (2004). “Understanding the Impacts of Anthropogenic Sound on Beaked Whales,” J. Cetacean Res. Manage. 7 (3), 177–187

Cranford, T. W. (1988). “The anatomy of acoustic structures in the spinner dolphin forehead as shown by X-ray computed tomography and computer graphics,” in: Animal Sonar: Processes and Performance, P. E. Nachtigall and P. W. B. Moore, eds., (Plenum, New York) pp. 67–77.

Cranford, T. W. and Amundin, M. E. (2003). “Biosonar Pulse Production in Odontocetes: The State of Our Knowledge,” in Echolocation in Bats and Dolphins, J. A. Thomas, C. F. Moss, and M. Vater, eds. (The University of Chicago, Chicago) pp. 27–35.

Cranford, T. W., Amundin, M., and Norris, K. S. (1996). “Functional morphology and homology in the odontocete nasal complex: Implications for sound generation,” J. Morphol. 228, 223–285.

Cudahy, E. A., Hanson, E., and Fothergill, D. (1999). “Summary on the bioeffects of low-frequency waterborne sound,” in Technical Report 3, Environmental impact statement for surveillance towed array Sensor system low-frequency active (SURTASS LFA) sonar.

Finneran, J. J. (2003). “Whole-lung resonance in a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas),” J. Acoust. Soc. Am. 114 (1), 529–535.

Frantzis, A. (1998). “Does acoustic testing strand whales?,” Nature (London) 329, 29.

Fraser, F. C. and Purves, P. E. (1960). “Hearing in cetaceans: Evolution of the accessory air sacs and the structure and function of the outer and middle ear in recent cetaceans,” Bulletin of the British Museum (Natural History) Zoology 8, 1–140.

Garner, E., Lakes, R., Lee, T., Swan, C., and Brand, R. (2000). “Viscoelastic dissipation in compact bone: Implications for stress-induced fluid flow in bone,” ASME J. Biomech. Eng., 122 (2), 166–172.

Hildebrand, J. A. (2005). “Impacts of Anthropogenic Sound” in Marine Mammal Research: Conservation beyond Crisis, J. E. Reynolds et al., eds. (The Johns Hopkins University Press, Baltimore, Maryland).

Myers, M. R. (2004). “Transient temperature rise due to ultrasound absorption at a bone/soft-tissue interface,” J. Acoust. Soc. Am. 115 (6), 2887–2891.

NOAA (2001). “Joint Interim Report Bahamas Marine Mammal Stranding Event of 14-16” March 2000. Washington, D.C., US Department of Commerce and US Navy, available at: www.nmfs.noaa.gov/prof-res/overview/Interim-Bahamas-Report.pdf.

Norris, K. S. (1964). “Some problems of echolocation in cetaceans.” in Marine Bio-acoustics W. N. Tavolga, ed (Pergamon Press, New York) pp. 317–336.

Rommel, S. A., Costidis, A. M., Fernandez, A. J. F., Jepson, P. D., Pabst, D. A., McLellan, W. A., Houser, D. S., Cranford, T. W., van Helden, A. L., Allen, D. M., and Barros, N. B. “Elements of beaked whale anatomy and diving physiology, and some hypothetical causes of sonar-related stranding,” J. Cetacean Res. Manage., in press. (Link)

Soldevilla, M. S., McKenna, M. E., Wiggins, S. M., Shadwick, R. E., Cranford, T. W., and Hildebrand, J. A. (2005). “Cuvier’s beaked whale (Ziphius cavirostris) head tissues: Physical properties and CT imaging,” J. Exp. Biol., 208 (12), 2319–2332. (Link)

Sunderland, S. (1978). Nerves and nerve injuries, 2nd ed. (Churchill Livingstone, Edinburgh).

Wagner, M., Gaul, L., and Dumont, N. A. (2004). “The hybrid boundary element method in structural acoustics,” Z. Angew. Math. Mech. 84, No. 12, 780–796.

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The seaquake theory to explain the centuries-old mystery of why whales mass beach themselves is the originally creation of Captain David W. Williams and registered with the Writer's Guild of America—Reg. No: 10608118. The reproduction and use of any part or all of this intellectual creation in any form, including film, is strictly prohibited. In particular, no part of these web pages may be distributed or copied for any commercial purpose. No part of this intellectual property may be reproduced on or transmitted to or stored in any other website, or in any other form of electronic retrieval system or used in any film or book; however, you may link to this website without permission. Reference this web page as the source when quoting. Send email request for any other use.