US Navy Admits Its Sonar Killed Whales
By Cat Lazaroff
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.
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 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."
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.
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.
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.
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.
The interim report is available online at: http://www.nmfs.noaa.gov/prot_res/overview/Interim_Bahamas_Report.pdf
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