(ENS) WASHINGTON --
U.S. Navy has been given permission to "harass marine mammals" in the course of operating low frequency sonar used to detect submarines while remaining outside the range of their onboard weapons. The Navy has been approved to deploy two ships that use the sonar system in spite of continuing controversy over whether the loud signals it emits injure whales, dolphins, seals, and turtles.
After reviewing more than 10,000 public comments on the issue, the National Marine Fisheries Service Monday exempted the Navy from provisions of the Marine Mammal Protection Act even though the service acknowledged that the sonar "has the potential to affect marine mammals."
Under this authorization, the Navy will be able to operate up to two Surveillance Towed Array Sensor System Low Frequency Active Sonar (SURTASS LFA) systems over a five year period. The exemption is subject to annual review.
The agency said the sonar will have "no more than a negligible impact on the affected species," and "will not have an unmitigable adverse impact on the availability of these species or stock(s) for subsistence uses."
The Natural Resources Defense Council is considering a lawsuit to block the exemption, spokesman Michael Jasny told reporters July 15. The group's campaign against the LFA sonar led to the Navy's 1999 request for an exemption to the Marine Mammal Protection Act.
LFA sonar has not been operated since research in preparation for this authorization concluded in late 1998.
According to the Navy, the LFA system has 18 projectors, or sound sources, each capable of transmitting sound at a level of approximately 215 decibels (dB) between 100 and 500 Hz.
"Because it is an array, if one looks at LFA from a distance, it will appear to have an effective source level on the order of 230 to 240 dB. However, in the actual water column, no portion of the ocean will experience sound levels greater than 215 dB," the Navy says.
By comparison, an Air Bus A320 taking off is measured at 87.8 decibels, and a rocket engine at 180 decibels. Because the decibel scale is logarithmic, not linear, a loudness of 230 decibels is many times louder than 180 decibels.
Permanent hearing damage in humans is caused at 150 decibels, and the Navy acknowledges that sounds louder than 180 decibels could cause injury to marine mammals or other marine life.
The current plan is for two vessels to have this sonar system, one in the Atlantic, the other in the Pacific. Each vessel would be underway at sea for up to 270 days per year, each moving at three knots, transmitting less than 20 percent of the time, the Navy states.
The Ocean Conservancy, Washington, DC based oceans advocacy group, said Tuesday that the fisheries service lacks the scientific knowledge to issue such a permit and cannot demonstrate that LFA sonar technology will have a negligible impact on marine mammal populations.
̉The ability to detect sounds within their environment is extremely important to marine mammals. Anything that impedes the ability of an animal to detect important acoustic cue within their environment can have a significant impact on basic life functions, such as finding food or mates, reproducing, and caring for offspring," says Nina Young, director of marine wildlife conservation at The Ocean Conservancy.
The Navy has tested LFA technology on only three of the more than 48 marine mammal species that may be affected by it, the Ocean Conservancy says, and scientists lack "accurate abundance estimates, natural history information, and data on geographic distribution, migratory routes, and calving and breeding grounds."
Sublethal impacts, or as the Navy puts it "non-serious injury," may be as devastating as lethal impacts, says Young, "causing death by impairing foraging or predator detection, but the potential for these types of extended or delayed impacts from any sound source are not well understood for any mammal, and have not been adequately studied by the Navy."
Fisheries officials have placed conditions on the approval to prevent the potential for injury to marine mammals and sea turtles.
The Navy will conduct visual monitoring, and both passive and active sonar monitoring, to ensure that marine mammals and sea turtles are detected before they enter the area where LFA sonar would be used. The Navy must shutdown the LFA sonar whenever marine mammals or sea turtles are detected.
"Detection is expected to be almost 100 percent effective up to two kilometers (1.1 nautical miles or 6,562 feet) from the sound source. It has been determined that at one kilometer, the LFA sound has diminished to a level that would not cause harm to marine mammals," the fisheries agency says.
The Navy must limit the upper frequency of LFA sonar to 330 Hz to prevent non-auditory injury.
And the Navy is prohibited from using SURTASS LFA sonar within 12 nautical miles of all coastlines and in designated marine mammal biologically important areas.
But the Ocean Conservancy says the scientific research is not in place to provide protection for marine mammals. "The acoustic behavior, auditory sensitivity, and frequency range of many marine mammal species are virtually unknown," Young says. Hearing curves are only available for approximately 12 species of marine mammals and there are no published audiometric data for many other whale species such as beaked, sperm and humpback whales.
The Natural Resources Defense Council says that whales use "their exquisitely sensitive hearing to follow migratory routes, locate one another over great distances, find food and care for their young. Noise that undermines their ability to hear can threaten their ability to function and survive."
The potential long term impacts that the Navy's LFA system might have on the behavior and viability of entire populations of marine mammals is of concern to conservationists and marine scientists.
Sound has been shown to divert bowhead and gray whales and other whales from their migration paths, to cause sperm and humpback whales to cease vocalizing, and to induce distressed behavior and even panic, the NRDC says.
The SURTASS LFA authorization requires the Navy to investigate several questions left unanswered by previous LFA research, including responses of sperm and beaked whales to LFA signals, behavioral responses to sub injurious sound levels, and long term silencing effect of LFA signals on whale calls.
"If this research discovers risks," says the fisheries service, "appropriate mitigation measures are to be developed."
The Navy says SURTASS LFA sonar is a crucial part of its ability to detect submarines, "the ultimate stealth weapons," at long distances, before they pose a danger to U.S. surface ships.
Currently there are 224 submarines operated by non-allied nations, "much quieter and more deadly than ever before," the Navy says. "An undetected enemy submarine is an underwater terrorist, threatening any surface ship or coastline within its range."
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