The Navy wants to deploy a global surveillance system to hunt for a
new generation of silent enemy submarines. But marine scientists and
environmentalists are fighting the proposal, saying it could prove lethal to
whales and other marine mammals.
A disturbing number of whale strandings last year near Navy sonar maneuvers
in the northern Bahama Islands, critics say, was just the latest evidence that
the system can disrupt whale migration routes, damage whale hearing and cause
hemorrhages in the brain.
For decades, the Navy has used sonar - the underwater equivalent of radar -
to hunt for submarines. The technology involves beaming a sound signal that
bounces off objects and sends back information to receivers.
The Navy's latest request involves a technology called "low frequency
active" sonar, or LFA. The system can scan hundreds of thousands of square
miles of ocean with sound in the way a huge spotlight would search on land.
At issue is what damage the sound can do to animals that depend on hearing
to live.
The technology is already approved by all states except California for use
in their coastal waters. But the Navy wants the go-ahead from the National
Marine Fisheries Service to deploy it beyond coastal waters. A decision is
expected within the next few months.
The Navy withdrew its application for use in California, where it faced
heavy opposition from the California Coastal Commission. Mark Delaplaine, a
program head at the commission, said the Navy had failed to show that the
technology would not harm marine mammals.
"Hearing to whales is what sight is to humans. Whales communicate thousands
of miles using low-frequency sound," Delaplaine said. "They've evolved to take
advantage of the fact that no one else uses that frequency. Using their niche
is sort of like tinkering with evolution. In a sense, we're using their turf."
The Navy started developing LFA in the 1980s, and has already used it in
two dozen tests around the world.
Navy officials say they need the technology because the passive sonar
systems of the past no longer work with new silent submarines. The decision on
whether or not to deploy the LFA system must balance environmental concerns
against national security needs.
In its latest proposal, the Navy wants to use four sonar ships in the
Pacific and Atlantic oceans. On each ship, an array of 18 loudspeakers, each
the size of a Volkswagen, hang into the ocean to a depth of about 200 feet.
Each ship's array operates at a frequency range of 250 to 500 hertz and
emits sound at 215 decibels. When the sound strikes an object, echoes return
and get picked up by a couple of hundred underwater microphones, trailing off
the back of the vessel. A computer determines if the object is a submarine and
how far away and how fast it's moving.
At close range, the sonar's noise level is well above the maximum level
considered safe for a whale's hearing, which according to the Navy is 180
decibels.
But the Navy says that beyond a kilometer from the sound array, the noise
drops below that level. The Navy says it plans to use observers to scout out
whales and other marine mammals and stop the operations when the animals are
within range.
The Navy acknowledges that the sound level may still be high enough to
disrupt whale migrations, which scientists say can occur at 120 decibels. Even
100 miles from the sound array, sound level would be from 150 to 160 decibels.
"There's a possibility that it could disrupt whale communication," said
Navy spokesman Lt. Douglas Spencer. " But these systems are operated for a
short period of time (about 430 hours a year) and they're mobile. It's highly
unlikely there would be a permanent long-term effect."
Indeed the Navy argues that the cumulative effects of LFA on marine mammals
would be extremely small. Particularly sensitive areas, such as marine
sanctuaries and a region of the East Coast used by northern right whales would
be off limits to the technology.
But critics say the Navy's studies to determine the effects on marine
mammals were flawed.
They complain that researchers studied only four species of marine mammals
for a month and tested decibel levels far below what the system would actually
deliver to ocean life.
"The Navy's conclusions that the low-frequency sonar will work are
premature and based on inadequate data," said Naomi Rose, a marine mammal
biologist at the Humane Society of the United States in Washington.
Some critics estimate that the LFA would produce a much higher sound
intensity than the Navy discloses. The effective source level of the system,
they say, might be somewhere between 230 to 240 decibels, the equivalent of
the sound generated by an exploding rocket.
Pinpointing the correct decibel levels is particularly important, critics
argue, because decibel levels are measured on a logarithmic scale: every
increase of 10 decibels means a 10-fold increase in intensity or power.
At close range, the noise that LFA produces is millions of times more
intense than the Navy considers safe for human divers (145 decibels) and
billions of times more intense than the level known to throw gray whales off
their migration routes (120 decibels), some marine scientists say.
Last year, an unprecedented stranding of 16 beaked and minke whales and one
spotted dolphin in the Bahamas occurred in the vicinity of a Navy sonar
testing maneuver. These strandings resulted in nine whale deaths.
Necropsies on six of the animals showed no signs of blunt trauma that might
have resulted from a collision with a vessel. But they did turn up signs of
brain hemorrhaging, which is consistent with injury from sound, said Darlene
Ketten, a scientist at Woods Hole Oceanographic Institute.
Kenneth Balcomb, founder of the Center for Whale Research in Friday Harbor,
Wash., and leader of the Bahamas Marine Mammal Survey, concluded that some
whales died from a vibration in their cranial air spaces that tore delicate
tissues around the brain and ears. The LFA sonar could cause the same damage,
he believes.
But Navy spoesman Lt. Spencer said that "we don't have enough data to
determine" what caused the strandings. Moreover, the sonar system the Navy
used in the Bahamas was a mid-range frequency sonar, not a low frequency sonar, and so the effects would be different.
Still, the whale strandings in the Bahamas triggered an outpouring of
concern about the Navy's proposal. Twenty-six congressional representatives
sent a letter urging that the Defense Department withdraw the project request.
And last month, 44 scientists representing 13 universities and research
institutions signed a petition also requesting a withdrawal and the creation
of an international panel to form regulations.
The Bahamas incidents have led some to speculate military uses of the sonar
technology might explain other mysterious strandings.
"The Navy could very well have been causing these kind of traumas all over
the world," Rose said. "Now comes a technology that is more likely to affect
baleen whales. It's as loud or louder. Because it's a lower frequency, it's
going to travel farther over a larger area. And it's never been out there
before."
©2001 San Francisco Chronicle
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