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Can sonar, sea life mix?

January 3rd, 2006 by admin in Conservation and Marine biology

US Navy wants underwater range, but many fear for whales.

Just as the U.S. Navy is gearing up to install a 660-square-mile sonar training range off the coast of North Carolina, evidence is mounting that sonar harms some whales.

Scientists link sonar to some fatal whale beachings, though they aren’t certain how the underwater sound causes trouble. Some suspect it can startle animals, making them surface so fast that they get the decompression illness known as the bends.

Environmentalists suspect that Navy sonar caused the rare beaching of three whale species in January 2005 on the Outer Banks. A federal National Marine Fisheries Service report expected as early as this month may or may not clear that up.

“There are so many hurdles to understanding the effects of sonar,” said Andy Read, a Duke University marine mammal biologist based in Beaufort. “There are many questions we can’t answer yet. The Navy can’t answer them yet either.”The Navy acknowledges that some whales, very rarely, can be harmed by sonar. But on the basis of research and computer models, it concludes that a proposed sonar off North Carolina would bother, but not injure, a fraction of the marine mammals out there.
Protective steps would reduce that risk to almost nothing, the Navy says. The plan calls for posting trained scouts on ship decks to watch for animals and listening underwater for the animals. The Navy would decrease the strength of sonar signals when creatures get too close.

“We expect some behavioral reactions, whether it will be the animals turning away to leave the area or exhibiting some disturbance. We expect nothing more than that,” said Aileen Smith, a Navy biologist and natural resources manager for the U.S. Fleet Forces Command in Virginia.

Navy’s plans for range

The Navy says it needs an Atlantic Ocean sonar range as a realistic training ground for sailors and pilots to detect a new generation of submarines. Powered by batteries and air-propulsion systems, the quiet vessels can sneak into coastal waters, unlike the deep-water subs the Navy chased during the Cold War.

A sonar system emits pulses of sound, which bounce off objects underwater. By analyzing the echoes, the Navy can detect and track what it cannot see. Sonar is a vital defense tool, but attention is growing to the technology’s unintended consequences.

With a federal court suit, environmentalists in 2003 forced the Navy to limit use of its most powerful (low-frequency) sonar to a portion of the Pacific Ocean. This fall, environmentalists filed a second lawsuit, asking a federal court to also restrict the Navy’s use of mid-frequency sonar, the kind envisioned for the training range off the North Carolina coast.

Mid-frequency sonar’s primary use is to detect enemy submarines nearby — within 10 nautical miles. If the range is built, sailors and pilots aboard surface ships, aircraft and submarines would use it to test and refine their detection skills.

The loudest sonar on the range would produce pings reaching 235 underwater decibels. Scientists are still developing scales to describe underwater noise, but 235 underwater decibels is louder than the song of a humpback whale, which a nearby human listener can hear — and feel — underwater. Sonar pings are sustained for only a few seconds, however, while whale sounds go on for minutes, which makes the effect louder, scientists say.

The Navy evaluated potential sonar range sites off North Carolina, Virginia and Florida. But it has long favored a patch of ocean 47 miles offshore of the Marines’ Camp Lejeune in Jacksonville. It’s at the edge of the continental shelf and in the path of the warm-water Gulf Stream. Waters there teem with many types of fishes, sea turtles, dolphins and whales.

Beachings not new

Unexplained whale beachings were recorded long before sonar came along. But the technology, developed in the early 1900s, is increasingly suspected as playing a role. Since the 1990s, scientists have linked mid-frequency sonar blasts to a small number of strandings of beaked whales, species that are less likely to beach than other whales. Some of those whales live off North Carolina.

“If someone had said years ago that mid-frequency sonar would be a problem, I would have said no. But these are documented, real issues,” said Paul Nachtigall, director of the Marine Mammal Research Program at the Hawaii Institute of Marine Biology.

Scientists tie mid-frequency sonar blasts to whale beachings in three Atlantic Ocean island groups — Madeira, the Canary Islands and the Bahamas. The Navy concedes that its sonar was a culprit in one incident, when 17 beaked whales stranded in the Bahamas in 2000. The military blamed narrow underwater channels, which limited where the animals could swim to escape the sound.

A 2003 report in the science journal Nature found that some of the 14 beaked whales that stranded in the Canary Islands in 2002 had internal injuries resembling damage from gas bubbles, a symptom of the bends. The Navy says that beaked whales may be a special case and identifies four species found off North Carolina as most vulnerable.

Navy efforts praised

Federal laws, including the Marine Mammal Protection Act and the Endangered Species Act, forbid the harming or harassing of whales and other sea mammals, including dolphins. So the National Marine Fisheries Service is reviewing the Navy’s plans to protect those creatures.

The agency is supportive of some of the analysis the Navy has prepared but is reserving judgment on other portions.

Steve Leathery, chief of the service’s protected resources permits division, praises the Navy’s sophisticated approach to estimating the decibel levels sonar sustains as it moves through sea water.

But the agency has not yet agreed with Navy estimates about how far dangerous levels of noise will travel from sonar equipment.

“We’re still working with them,” Leathery said.

The marine fisheries agency this month is expected to release a report exploring what caused the mysterious whale strandings on the North Carolina coast last winter. At least 37 whales washed ashore in mid-January near Oregon Inlet. Most were pilot whales, but one was a newborn minke whale and two were dwarf sperm whales.

Environmentalists say mid-frequency sonar used by the USS Kearsarge Expeditionary Strike Group during offshore exercises may be at fault. The Navy says it wasn’t close to shore and sees no connection.

Environmental groups have sued marine fisheries to get access to the data it collected after that stranding, along with strandings elsewhere.

The fisheries service is also scrutinizing the Navy’s conclusion about the dangers its range will pose to giant North American right whales. One of the biggest threats to these animals, which number about 320, are collisions with ships.

One pregnant right whale washed up dead on the Outer Banks two years ago after being struck by a ship. Two right whales have been spotted entangled in fishing gear off the state’s coast in the past two years, including one last month. In both cases, the animals evaded rescuers.

The Navy maintains that a sonar range off North Carolina could possibly disturb — not harm — only two officially endangered whales species: humpbacks and sperm whales. It concludes that right whales hug too close to the shore on their trips up and down the North Carolina coast to be put in any peril by sound.

The Navy says that ships and other vessels using the range will need to be on the lookout for right whales while traveling from ports to the north and south.

But scientists say the Navy may be overly optimistic that right whales will be too far away to be bothered by sonar. Their whereabouts are not always clear, and biologists who study them can’t say exactly where the creatures travel off the coast.

Recent sightings suggest waters off North Carolina may be more important to right whales than previously known. A year ago, UNC-Wilmington biologists documented a right whale and what looked like a newborn calf near Johnnie Mercer’s Fishing Pier on Wrightsville Beach. That raises the possibility that the whales give birth closer to shore than previously thought.

Also, Doug Nowacek, a Florida State University biologist, has conducted sound studies on right whales. Some, he said, get startled by sound and move to the surface and stay there. If right whales are bothered by sonar, they could place themselves in greater danger of colliding with a ship if startled, he said.

“This certainly has the potential to significantly disrupt or harm those animals,” Nowacek said.

The marine fisheries service is “taking a hard look” at the Navy’s claims about right whales, said Leathery, the service’s section director.

Other possible risks

In recent weeks, the Navy learned that some North Carolinians are skeptical about claims that a sonar range would be harmless to fin fish, as well.

The N.C. Division of Marine Fisheries has criticized the Navy for underestimating the risk a range would pose to coral reefs, vital habitat to many fishes. The state fisheries agency also says the Navy has ignored scientific findings that sound can frighten and even damage some fish.

The Navy has promised to work up more data on those questions but says research and experiences with sonar in the Pacific Ocean indicate negligible risks.

If a Navy range does get built off North Carolina, scientists say it might clear up some mysteries.

Read, the Duke University biologist, is among a group of North Carolina researchers trying to land a contract with the Navy to monitor animals moving through the range site before and after exercises start there.

In an ideal world, Read said, he would prefer that sonar not get sounded regularly off North Carolina’s shore, since it might put wildlife at risk. But if it happens, he said, monitoring might at least shed new insight on what sonar does.

“Should they conduct this in one area as opposed to doing it all over the place like they are doing now? I would prefer that,” Read said.

source: newsobserver.com