April 18, 2004

Since our visit to the European Parliament last summer on this issue new evidence indicates that the effects of high intensity active sonars (including LFAS) on marine life are more serious than we previously reported.

High Intensity Active Sonar Update (2003)

The US Navy and other navies are planning to operate potentially lethal high-intensity active sonars, including Low Frequency Active Sonar (LFAS) in 75% of the world's oceans. LFAS has never been officially tested at exposure levels above 155 dB which is about one-millionth the intensity of the proposed deployment source level. Recent disclosures indicate that the scope and risks of harm from LFAS are broader and more serious than previously understood. "The full scope of evidence regarding impacts on marine mammals (including a growing number of mass strandings) at exposure levels far below the proposed 180 dB injury threshold, and the serious risks that LFAS poses to fish and human divers have become public only within the last year" (Amended Plaintiff's Motion for Summary Judgment Case Number CO2-3805 EWL, USA). According to the US Navy, signals from LFAS can still be 120 dB, a sound level causing avoidance behavior in whales, up to 1,111 km away from the deploying vessel. Since the sounds spread in all directions the signal from one vessel ensonifies a very large area of the ocean.

Marine Mammals

Necropsy reports show that injuries from mid-frequency sonars have caused whales to strand and die most notably in the Bahamas (2000) and the Canary Islands (2002). In fact, mid-frequency sonar appears to have devastated the Bahamas beaked whale stock as a whole. Most recently, other incidents of cetacean strandings or deaths coincident with naval exercises have been discovered including: Vieques, 1998 & 2002; Madeira, 2000; US Virgin Islands, 1999; Greece, 1996; the Canary Islands 1985, 1986, 1988, 1989 and the northwest coast of the US (2003). While the effect on marine mammals is more serious than previously thought, the extent of the problem is not known since both low and mid-frequency sonars and low frequency seismic air guns have been implicated. Evidence indicates that not all seriously injured animals strand; some die at sea, sink and are usually not discovered.


The adverse impacts of LFAS extend beyond marine mammals. Studies not included in the U.S. Navy's Environmental Impact Study on LFAS indicate that low frequency sound, including low frequency sonar, has the potential to injure and kill a wide variety of fish at intensities well below the 180 dB level assumed by the Navy to be the threshold for injury. A study commissioned by the British Defense Research Agency cites that fish exposed to sounds of the same frequency and duration of the LFAS signal at levels above 160 dB suffered internal injuries, eye hemorrhaging, auditory damage and mortality. Fifty-seven percent of brown trout died after exposure to levels above 170 dB.

A study by Norway's Institute of Marine Research showed that trawl catch rates of haddock and cod fell 45-70% over a 2,000 square mile area while low frequency air guns were being used. Catch rates did not increase during 5 days surveyed after the air guns stopped. A study by McCauley indicates damage to fish ears may begin at 160 dB with much shorter exposures than the LFAS signal. Thus, LFAS poses a significant threat to the already depleted fish stocks throughout the world's oceans.

Human Divers

Impacts of active sonar on human divers are also more severe than originally presented. The likelihood of panicked behavior in unalerted recreational divers exposed to LFAS has been recognized by doctors in the US Navy as a serious concern. The Navy's tests of LFAS on their own alerted personnel indicate that fairly strong aversive behavior would be expected at exposures well below 145 dB. Exposure to LFAS poses risks to recreational divers hundreds of miles from the LFAS source.

Effectiveness of LFAS is Questioned

Finally, the effectiveness of LFAS in accomplishing its major mission of detecting quiet submarines in shallow, confined waters has not been demonstrated and is questioned in a report by the US Congressional General Accounting Office (GAO). The US Department of Defense concurred with the findings of the GAO. Experts point out that while LFAS can locate submarines in deep, open waters, there already are safe, effective systems for doing that.


A US federal Court in August, 2003 recognized the dangers of LFA Sonar and issued an injunction on the peacetime use of this sonar. The injunction was tailored to reduce the risk to marine mammals and endangered species by restricting the sonar's use in areas that are particularly rich in marine life. What is clear is that the use of high intensity active sonar technology is expanding. Low-frequency active systems are being developed by the U.S. and Australian navies, and by member states of the European Union such as France, Germany, Great Britain, and the Netherlands. A number of other systems, including the mid-frequency system that has been implicated in several mass stranding events, are being deployed, tested, or reconditioned for use in coastal waters, which contain critical habitat for marine mammals and other ocean life. We are deeply concerned about the cumulative and synergistic environmental impacts that all of these systems, operating independently, might have.


Engas, A., Lokkeborg, S., Ona E. and Soldal, A. V. 1993. Effects of seismic shooting on local abundance and catch rates of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Canadian Journal of Fisheries and Aquatic Science, 53:22 38-2249.

McCauley, R.D., J. Fewtrell, A.J. Duncan, C. Jenner, M.-N. Jenner, J.D. Penrose, R.I.T. Prince, A. Adhitya, J. Murdoch, K. McCabe 2000. Marine seismic surveys: analysis and propagation of air-gun signals; and effects of air-gun exposure on humpback whales, sea turtles, fishes and squid. Report prepared for Australian Petroleum production Exploration Association by Curtin University of Technology (R99-15).

Turnpenny, A. W. H., Thatcher, K. P. and Nedwell, J. R. 1994. The effects on fish and other marine animals of high-level underwater sound. Report prepared for UK Defense Research Agency. (FRRI 27/94).

Prepared by: Marsha L. Green PhD - Ocean Mammal Institute

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