Bahamas beaked whale strandings (fwd)

From: pita admininstrator (
Date: Mon Dec 04 2000 - 19:39:58 EST

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Date: Mon, 4 Dec 2000 13:54:27 -0800
From: MARMAM Editors <marmamed@UVic.CA>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Bahamas beaked whale strandings (fwd)

The following are two press/information releases provided by the
U.S. Navy regarding the investigation into the beaked whale
strandings in the Bahamas


Update of the ongoing investigation into the stranding of Beaked Whales

15 November 2000

The U.S. Navy is continuing to assist the National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration, and Marine Mammal Commission in determining the cause of the mass stranding of beaked whales in the Bahamas on March 15th of this year. Navy contributions to this ongoing analysis include a thorough review of sound propagation features that would have affected SONAR sounds made by U.S. Navy ships that transited Northwest Providence Channel in the Bahamas just prior to the whale strandings. The detailed acoustic analysis of the SONAR operations of the Navy ships will provide additional data that may be useful in the assessment of any connection between the strandings and Navy operations. The Navy is working closely with all concerned agencies and will continue to refine the acoustic data and models to be combined with other ongoing research expected to be completed by summer of 2001. Simultaneously, NMFS is conducting an examination of the recovered marine mammal specimens to determine what trauma, if any, occurred and what caused the animals to beach themselves.

The analysis of the acoustic fields present in the New Providence Channel on the day of the strandings last March was done by the Navy Undersea Warfare Command (NUWC) and the Office of Naval Research (ONR) as part of the Navy's overall investigative effort led by the Commander in Chief of the U.S. Atlantic Fleet. This acoustic modeling uses state-of-the-art technology and was validated by a panel of independent scientists and experts in the fields of oceanography and underwater sound.

The Navy's acoustic analysis, which has been shared with NMFS and the MMC, addressed the sound pressure levels created by the ships' SONARs. The detailed analysis confirms the preliminary analysis conducted by NUWC that was discussed in June of this year. A surface duct was present in the New Providence Channel at the time of the stranding. A surface duct is a phenomenon in which sound energy is contained mostly within a surface layer of the ocean. It is the result of particular vertical distribution of sound velocity in the water that is typical of early spring conditions in many parts of the world. Within the duct, the sound propagates further than it does at lower depths.

The Navy analysis included a thorough examination of the environmental conditions that affect sound propagation. For purposes of the computer modeling effort, conservative values were used to ensure that the models did not underestimate the propagation ranges. At the same time, source levels of the Navy ships' SONARs were estimated at the maximum levels they are capable of producing at their reported operational modes. Consequently, any condition that could not be confirmed from the on-scene, real-time observations of the ocean at the time of the stranding was given a value that was ideal for sound transmission. Factors that would have weakened sound propagation were excluded from the analysis. As noted earlier, the Navy's analysis of the sound field has addressed the sound pressure levels and propagation ranges from the ships' SONARs in the Channel. The Navy is now exploring whether the acoustic modeling effort will be able to analyze other acoustic characteristics from associated with the SONARs, such as the repetitive rate of active transmission. The Navy is also considering additional research on beaked whales to learn more about the effects of acoustic energy on these unique deep diving mammals. The Navy is committed to continue its program of marine mammal research, and as part of that research, to specifically address whether, and in what circumstances, midrange operational SONARs may pose a risk to beaked whales.

The Navy is the worldwide leader in funding research into the effects of sound on marine mammals. That research is conducted to ensure essential naval operations and systems---such as SONAR---are operated with minimal impacts upon marine mammals. The proliferation of quiet, diesel-electric submarines operated by unfriendly nations and competitors constitutes one of the top naval threats to the United States and its allies. Unlike the blue-water submarines and cold-war tactics of former Soviet navies, those submarines are operated in the world's littoral regions and ocean choke points --- areas that are vital to international commerce, peace, and stability.

This year the Navy increased its research budget on this topic by more than 50 percent (to more than 3 million dollars, annually). ONR programs, including this one, are reviewed frequently by external peer panels, including the National Academy of Science. All work is unclassified and researchers are encouraged to publish their findings in open, peer-reviewed literature. Research projects from 1999 and 2000 can be found at

If, either as a result of the investigation into the Bahamas stranding or future research, it is determined that mid-range frequency, tactical Navy SONARs can produce traumas in beaked whales or any other marine life under identified conditions, the Navy will reassess its management and use of those SONARs in the course of peacetime training.



Navy Pinpoints environmental conditions during whale strandings

By Suzanne Yohannon

The Navy, in a detailed acoustic analysis, has found certain environmental conditions existed when Navy ships transiting through the Bahamas last March used active sonar systems at the same time over a dozen whales beached themselves on islands nearby. The use of Navy sonar systems under these environmental conditions may have affected whales in the area, the National Oceanic & Atmospheric Administration's National Marine Fisheries Service says in a Nov. 15 press release.

The findings could have implications for the Navy's use of active sonar, which it frequently employs in training operations worldwide.

The Navy and the fisheries service last week released information from a detailed Navy analysis of a computer model that confirmed the presence of a "surface duct" in the New Providence Channel at the time the whales stranded. Surface ducts affect how sound travels. The analysis examined the acoustic field that was created by several ships' sonar systems last March and included a thorough look at the environmental conditions that affect sound travel, according to the fisheries service. Five ships and one submarine using sonar were transiting through the channel at the time. The ships were using sonar at a power output of 235 decibels, at mid-range frequencies of 3,500 to 7,500 hertz.

A surface duct is a natural phenomenon that often occurs in the early spring. Within the duct, sound travels further at the surface than it would if a duct weren't present, according to the Navy and the fisheries service. Also, sound travels further at the surface than at lower depths, they say. The Navy presented the detailed analysis to the fisheries service Oct. 27, a Navy spokesman says.

"While this analysis does not answer all questions, it is possible that the Navy tactical sonars, particularly in the surface duct, caused effects to beaked whales that would otherwise not have occurred," the fisheries service says in the press release. The Navy doesn't go quite as far in its Nov. 15 press statement, saying that its detailed acoustic analysis of sonar operations "will provide additional data that may be useful in the assessment of any connection between the strandings and Navy operations."

Beaked whales were the predominant marine mammal that stranded on beaches in the Bahamas from March 15-17. A total of 16 marine mammals stranded, 10 of which were beaked whales - reclusive, deep diving whales of which little is known. Seven of the whales died, and post-mortem examinations of several of them indicated evidence of auditory trauma (Defense Environment Alert, June 20, p22). The fisheries service, however, says it "is still not possible to attribute the biological damage to a specific source of acoustic energy or pressure." But the service has ruled out volcanic eruptions, underwater landslides, other Navy tests or an explosion. It is continuing a detailed examination of the marine mammal specimens that it hopes to finalize in a report by next summer.

The next step for the Navy is to analyze whether the computer model can take into account other acoustic characteristics, such as the repetitive rate of sonar - which involves short pings at timed intervals - and the overlapping of several sonars in use at the same time, the Navy spokesman says.

The Navy in its press statement reiterates that it will reassess its use of sonars during peacetime training if the investigation or further research reveals that mid-range frequency, tactical Navy sonars can produce trauma in marine animals.

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