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Low-frequency bararge threatens sea life
by Nathan LaBudde
The oceans are vast, dark habitat for whales and dolphins who rely on sound much as people rely on on sight to carry out their primary life functions, from communication to finding food and escaping danger. The US Navy is now pursuing deployment of a secret submarine detection system that threatens to disrupt these animals acoustic ability.
The end of the Cold War brought a close to the US Navy's games of cat and mouse with Russian submarines. Today, the US is spending $64 billion to develop Virginia-class attack submarines to counter a phantom opponent.
The navy uses tactical formation s of battleships, aircraft carriers, destroyers, and the like, called carrier groups. While carrier groups visiting ports of call around the world provide political benefits reminiscent of Roosevelt's Great White Fleet's, naval strategists fear that larger, slower vessels in coastal waters are vulnerable to new small, hard-to-detect submarines. Current passive detection technology is said to be inadequate. Enter Surveillance Towed Array Sonar System., Low Frequency Active (LFA), which blasts low-frequency (100 -1000Hz) high-decibel noise and interprets the echoes. LFA sonar is of such magnitude, 235dB to 280dB, that any living thing - fish, sea turtles, marine mammals, humans - in the target area would likely find the noise lethal. Whales show an aversion to man-made sounds starting at 120dB, and the noise pain threshold for whales may be 170dB at half a mile.
To begin understanding the role sound plays in the life of a marine mammal and why disruption is dangerous, one need only consider the following: For millions of years, populations of humpbacks have been singing similar songs to one another over thousands of miles of open ocean. Over a season, a distinct version of the humpback song is repeated. Parallel changes spread through the population until all are singing a new song.
From 1980-95 the Navy tested LFA for some 7,500 hours without regard for the United States' environment laws. Pressure from environmental groups finally forced the Navy to undertake a field study in 1997-98 to comply with the Endangered Species Act, Marine Mammal Protect Act, and National Environmental Policy Act. It studied behavioral impacts on whales from a simulated LFA sound source for an environmental impact assessment (EIA) before authorizing four LFA ships (one is already under construction) and actual LFA deployment. The Navy hired two civilian whale acoustics experts, Dr. Christopher Clarke of Cornell University (no relation - ed.) and Dr. Peter Tyack of Woods Hole Oceanographic Institute.
The initial phase studied blue and fin whales. For eight weeks the Cory Chouest, outfitted with a tower of underwater LFA "speakers", transmitted 140dB omni-directional sound pulses every eight seconds for ten minutes at a time, while aerial and shipboard spotters observed whale behavior over a 119-square-mile area. Observers weren't told when the LFA source was transmitting. The sample group was extremely small, during a season when most blue whales have gathered farther north. Tests were hampered by inclement weather and scratched test days. During the testing periods of a pod of forty fin whales was seen "racing across the surface of the water," an event previously unseen and unknown by veteran whale researchers. Blue whales' vocalizations decreased by half and fin whales' by a third when the sound was broadcast.
Phase two studied the effects of LFA sonar on California gray whales migrating to their birthing and wintering lagoons in Baja California. When the sound source was turned on, whales coming within six-tenths of a mile of the 185dB sound source moved as much as a mile laterally to avoid it. It remains to be seen how the disturbance, if made routine, would affect the gray whales' annual 5,000-mile migration, one of the longest of any animal on Earth.
The final test was conducted in Hawaiian waters north of Kona, on humpback whales. Four-fifths of singing humpback whales stopped singing when exposed to the sound. Many humpbacks left the test area during the experiment: one whale-watcher suspended operations for lack of humpbacks. During the month-long test period, members of the Hawaii Ocean Mammal Institute documented instances of abandoned cetacean calves. A humpback whale calf, a three-week-old dolphin, and a melon-head whale calf were all seen in the test area. "We have never observed or heard of anyone observing an abandoned calf in our nine years of research of the Hawaiian Islands," says OMI's Marsha Green. "That these abandoned calves appeared only in the test area and nowhere else suggests... further investigation. The sonar tests may cause disorientation so the mother and calf become separated and then cannot fine each other"
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