WASHINGTON — The mysterious stranding of about 100 melon-headed whales in a shallow Madagascar lagoon in 2008 set off a rapid international response — a few of the eight- to 10-foot marine mammals were rescued, necropsies conducted, a review panel formed.
Did they follow prey into the lagoon? Were they sick? Was it the weather, or chemical toxins?
The panel recently gave its best answer, and it is causing ripples of concern. For the first time, a rigorous scientific investigation has associated a mass whale stranding with a kind of sonar that is widely used to map the ocean floor, a finding that has set off alarms among energy companies and others who say the technology is critical to safe navigation of the planet’s waters.
The independent review panel appointed by the International Whaling Commission concluded Sept. 25 that a high-powered, “multi-beam echosounder system” (MBES) was “the most plausible and likely behavioral trigger” for the stranding. About 75 of the animals, which normally inhabit deep ocean waters, died.
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A contractor for Exxon Mobil was using the sonar system — which sends “ping” sounds from a vessel toward the ocean floor — in a channel between Mozambique and Madagascar to determine where an oil and gas exploration rig might be safely constructed.
Computers use the returning echo from the pulses of sound to map the ocean floor.
The panel of five scientists “systematically excluded or deemed highly unlikely” nearly every other possibility before settling on the use of the MBES, which previously was considered relatively benign, according to the group’s report.
“The evidence seems clear to us that [the MBES] was pretty likely” the cause, said Brandon Southall, the panel’s chairman and a marine biologist at the University of California at Santa Cruz.
Exxon Mobil, which helped select the panel and partly funded the rescue of some of the whales in 2008, rejects the conclusion, contending the evidence is too flimsy for a determination that could have a far-reaching impact.
U.S. Navy sonar has been implicated in harm to whales and dolphins, environmental groups contend. A federal judge last month ordered federal biologists to reconsider permits that could allow the Navy to kill or disrupt marine mammals during anti-submarine warfare exercises off the coast of the Pacific Northwest.