- WASHINGTON, DC (ENS) - The
U.S. Navy and the National Marine Fisheries Service have released a report
acknowledging the role that the Navy's experimental sonar played in the
deaths of 17 marine mammals in the Bahamas last year. The report is the
agency's first official admission that sonar may contribute to whale
beachings.
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- The interim report finds that the March 2000 stranding
of 16 whales and a dolphin on Bahamian beaches was caused "by the
unusual combination of several contributory factors acting
together."
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- The Navy and NMFS concluded that the presence of the
whales in a restrictive ocean channel, during calm water conditions which
reflect and amplify sounds, caused the Navy's sonar to damage the whale's
ears, leading them to beach themselves.
-
- "Review of passive acoustic data ruled out volcanic
eruptions, landslides, other seismic events, and explosive blasts,"
the agencies reported. "The unusual extended use of Navy midrange
tactical sonars operating in the area is the most plausible acoustic
source."
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- The report says that the Navy's experimental Low
Frequency
Active Sonar (LFAS), which has been implicated in other whale strandings,
was not involved in this incident.
-
- Instead, the whales were injured because the calm water
and the underwater topography concentrated sound in the top 200 meters
of the ocean - just where the whales and dolphins would have been
swimming.
-
- "The calm seas did little to stop the reflection
and caused fewer air bubbles, which dissipate sound energy," the
report
notes.
-
- On March 15 and 16, 2000, nine Cuvier's beaked whales,
three Blainville's beaked whales, two unidentified beaked whales, one
spotted
dolphin, and two Minke whales were reported stranded along the Northeast
and Northwest Providence Channels on the Bahamian Islands. The strandings
took place within 24 hours of the intensive use of active midrange sonar
by U.S. Navy ships as they passed through the Northeast and Northwest
Providence
Channels.
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- The Navy says that multiple sonar units were used over
an extended period of time.
-
- Six of the whales died after stranding on beaches. One
dolphin stranded and died of unrelated causes. Ten whales were returned
to the sea alive.
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- Specimen samples were collected from four dead whales.
Three of these whales showed signs of bleeding in the inner ears and one
whale showed signs of bleeding around the brain.
-
- Whale biologists determined that the most likely cause
of the bleeding was either a blow to the head or exceptionally loud
noises.
-
- "The investigation team concludes that tactical
mid-range frequency sonars aboard U.S. Navy ships that were in use during
the sonar exercise in question were the most plausible source of this
acoustic
or impulse trauma," the report concludes.
-
- The investigation team recommended that future research
focus on identifying where combinations of ocean and undersea conditions
might combine to create similar problems in the future.
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- "This research, along with other research on the
impacts of sonar sounds on marine mammals, increased knowledge of marine
mammal densities, increased knowledge of causes of beaked whale strandings,
increased knowledge of beaked whale anatomy, physiology and medicine, and
further research on sonar propagation, will provide valuable information
for determining which combinations of factors are most likely to cause
another mass stranding event," they conclude.
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- Little is known about deep sea whales like this
Blainville's
Beaked Whale (Photo courtesy Cetacea)
-
- The team recommended that the Navy continue to
investigate
how sonar affects marine mammals and to develop measures to protect animals
"to the maximum extent possible and not jeopardize national
security."
-
- The Navy said it will include, when possible, Bahamian
scientists and other qualified individuals in future surveys involving
marine mammal research in Bahamian territorial waters.
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- The interim report is available online at:
- http://www.nmfs.noaa.gov/prot_res/overview/Interim_Bahamas_Report.pdf
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- Environment News Service (ENS) 2001.
All Rights Reserved.
- http://ens-news.com/ens/dec2001/2001L-12-21-07.html
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