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is comparable to bomb explosions. The navy estimated that
approximately 2,000 cetaceans (whales and dolphins) died
from exposure to sonar and more than 5  million suffered
some degree of hearing loss after training exercises. The navy
estimates that even from 300 miles away, a sonic blast is 100
times stronger than marine mammals can withstand. Deaths
of animals, especially cetaceans, often occur hours after expo-
sure to extremely loud underwater noise. For example, whales
die after beaching themselves shortly after a tactical sonar
exercise; this is a rather common occurrence that has been
reported in Greece, Madeira, Hawaii, Spain, and the coastal
United States—areas where sonar exercises are common. In
March 2000, at least 17 whales stranded themselves in the
Bahamas, and a federal investigation identified testing of a US
Navy active sonar system as the cause. Upon examination of
the whale carcasses scientists discovered blood on their brains,
ruptured ear canals, and bubbles in their systems similar to
when people contract decompression sickness (the bends).
Beaked whales are the most common ones affected. Scientists
attached digital devices to Cuvier's beaked whales off the coast
of California to measure the noise they were exposed to and
their response. When a simulated sonar signal was sounded at
200 dB and between 3 km and 10 km away, the whales stopped
feeding and swimming, swam rapidly away from the noise,
and some performed unusually deep and long dives.
Chronic effects of lower level exposures are also seen.
Marine biologists have linked the loud noises to reduced
vocalization, which suggests reduced communication, forag-
ing, and breeding. Humpback whale song in the Stellwagen
Bank National Marine Sanctuary was reduced during trans-
missions of an Ocean Acoustic Waveguide Remote Sensing
experiment approximately 200 km away.
Other animals are also sensitive. Giant squid were found
dead along the shores of Spain in 2001 and 2003 following the
use of air guns by offshore vessels; autopsies indicated that
the deaths were related to excessive sound exposure. A study
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