Beached whales likely killed by active sonar

Mike Holt

Sound travels very differently through water than through air, and little is known about the effects of noises of varying pitches and intensities on aquatic organisms 1. Ocean water transmits some frequencies of sound much more readily than others—rain falling on the surface can be heard up to a mile deep where some seemingly louder noises from passing ships are undetectable—but all sound travels much farther under water than above. According to Jeff Nystuen of the Applied Physics Laboratory at Washington University, “we don’t really know what is too loud underwater, and we need to know what the baseline is.” The research of Nystuen and his colleagues as well as that of many other scientists today is focused on revealing the consequences of uncommonly loud noises on marine life, especially those originating from manmade sources such as active sonar, which is commonly used by construction crews, oil and gas companies, geophysical researchers, and naval vessels 2.


On 24 September 2002, an international naval exercise involving the use of mid-frequency military sonar took place in the waters off the coast of the Canary Islands. Four hours after the exercise commenced, stranded whales and dolphins began appearing on the beaches nearby. Of approximately 30 animals that washed ashore, 14 beaked whales arrived dead 3, which led the Spanish navy to abandon its participation in the exercise 1. Necropsies were performed on eight of these whales, and all specimens examined showed evidence of decompression sickness, or DCS 3, which is more commonly known as the bends in humans.


Beaked whales washed ashore in Canary Islands 7.

The bends is a condition common among deep-sea divers, especially those who surface too quickly from depth. It is caused by decompression of inert gases usually dissolved in the bloodstream, chiefly nitrogen, into the gaseous state 4. This induces the formation of gas emboli, or small air bubbles, in various body tissues, particularly in the liver and the bones, as they become supersaturated with nitrogen. In many beached whales from the past few decades, a necropsy of the liver revealed macroscopic emboli ranging in diameter from 0.2 to 6.0 cm, comprising anywhere from 5 to 90 percent of the liver’s volume. The presence of these hepatic lesions in the absence of pathogenic bacteria (as was found to be the case here) suggested the in vivo formation of gas emboli 3, which contradicts traditional dogma that marine mammals are immune to all forms of DCS.


a) Macroscopic gas-bubble lesions in liver of a common dolphin. Scale bar 10mm.
b) Gas bubbles in hepatic parenchyma. Scale bar 750μm 3.

Other cases of DCS in marine mammals have also been observed. In 2004 Michael J. Moore and George A. Early demonstrated osteonecrosis to be “a progressive condition in sperm whales” through the study of many deep-sea whale skeletons from the past century. Osteonecrosis is caused by the disruption of blood flow through bone tissue due to gas emboli, leading to the death of tissue and partial decay of the bones. Moore’s and Early’s findings suggested that “acute embolic disease may result from disruption of normal dive patterns” that would be associated with whales’ and dolphins’ reactions to sudden loud sounds 5.


Erosion in whale bones caused by gas bubbles.
Scale bar 2cm top panel, 1cm others 5.

Whales and dolphins belong to the order Cetacea; they are among mammals perhaps the most adapted to marine life. They can hold their breath underwater for extremely long periods of time, so they often dive deep into the ocean. Some cetaceans have the ability to echolocate; they navigate the waters primarily by sound 6. These organisms are especially vulnerable to intensely loud noises. According to Dr. Mark Simmonds of the British Whale and Dolphin Conservation Society, cetacean echolocation organs “are particularly sensitive to high intensity noises. If they hear a sound that is distressing their natural reaction is to move away from it quickly. The frequency and volume of such sounds could be one factor pushing them into shallower waters.”

Consequently, in addition to damage attributable to DCS, evidence of trauma to auditory organs has been observed in post mortem examinations of whales beached in the United Kingdom. Some specimens exhibited “damage and hemorrhaging to the echolocation organs, as if they had suffered an acoustic trauma 1.” This could readily have been caused by low- or mid-frequency active sonar, which can emit sound waves exceeding 235 decibels, roughly the equivalent in intensity of a Saturn V rocket during takeoff. These sound waves can travel as far as 300 miles, remaining as powerful as 160 decibels 100
miles from origin, potentially resulting in widespread disruption of surrounding ecosystems.



Beaked whale washed ashore in the Bahamas 7.

Evidence of the far-reaching damage of active sonar can be seen in the many other beaches where dead cetaceans have washed ashore with symptoms of rapid flight from sonar blasts. Such beached animals have appeared not only in the Canary Islands and Great Britain, but also in Madeira, Greece, Japan, the Virgin Islands, the Bahamas, Alaska, North Carolina, and the Pacific Northwest 7. Such widespread dispersion of decompression-related beachings has aroused much concern in the scientific community.

In recognition of this growing problem, the U.S. Congress created the Marine Mammals Commission advisory panel in 2003, which consisted of leading scientists as well as representatives from the various commercial and military industries that employ the use of active sonar. The panel’s purpose was to devise a plan for researching the effects of various noises on ocean life, but it dissolved after two years of meetings due to an inability to reach consensus, which according to MMC executive director David Cottingham was the result of the “high degree of uncertainty over the impact of various noises on marine mammals.”

Some former panelists and other individuals close to the proceedings, however, believe the panel’s dissolution was the result of interference by groups with particular interest in unrestricted sonar usage. For example, last year courts forced the U.S. Navy to release e-mail correspondence in which military officials conspired to pressure a scientist to withhold information about the effects of sonar on ocean life. In the words of marine mammalogist Hal Whitehead of Dalhousie University in Nova Scotia, Canada, “The science of ocean sound is highly politicized. I see the breakdown of the committee as an indication that the Navy and others didn't want Congress to have a clear picture of what the risks are 8.”

These risks, though perhaps obscured to members of Congress, are all too apparent to the scientific community. Though hindered by the lack of consensus by the MMC advisory panel, ongoing research continues to investigate the apparent link between active sonar and cetacean beachings. Until a further understanding of this relationship is reached, the Navy and others should be urged to minimize their usage of damaging sonar equipment, lest they unwittingly and irreparably devastate whole populations of sea life.

References:

  1. Barber, Simon (2006). Lost whales find their way to an early death. The Telegraph Newspaper Online. Retrieved 3 April 2006 from http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/03/06/nwhale06.xml&sSheet=/news/2006/03/06/ixhome.html.
  2. Godvin, Tara (2006). Scientists study sound, marine creatures. The Associated Press. Retrieved 3 April 2006 from http://www.usatoday.com/tech/science/2006-02-26-underwater-noise_x.htm.
  3. Jepson, P.D., Arbelo, M., Deaville, R., Patterson, I.A.P., Castro, P. Baker, J.R., et al (2005). Gas-bubble lesions in stranded cetaceans. Nature, 425, 575-576.
  4. Wikipedia Contributors (2006). Decompression Sickness. Wikipedia, The Free Encyclopedia. Retrieved 3 April 2006 from http://en.wikipedia.org/wiki/Decompression_sickness.
  5. Moore, M.J., & Early, G.A. (2004). Cumulative sperm whale bone damage and the bends. Science, 306(5705), 2215.
  6. Wikipedia Contributos (2006). Cetacea. Wikipedia, The Free Encyclopedia. Retrieved 3 April 2006 from http://en.wikipedia.org/wiki/Cetacea.
  7. National Resources Defense Council (2005). Protecting whales from dangerous sonar. Retrieved 3 April 2006 from http://www.nrdc.org/wildlife/marine/sonar.asp.
  8. Dalton, Rex (2006). Panel quits in row over sonar damage. Nature, 439, 376-377.