WASHINGTON, DC, December 21, 2001 (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.
A beached goosebeak whale somewhere in the Caribbean (Photo courtesy
Laboratorio de Mamíferos Marinos del Caribe)
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.”
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
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“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.”
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
The Navy says that multiple sonar units were used over an extended period of
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.
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.
“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.
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.