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infoshark - 16.08.2007, 12:17Sonar exercises essential despite whale risks: navy
Sonar exercises essential despite whale risks: navy
But in the wake of California ruling, captain says a ban might be feasible at certain times of year to protect orcas
Published: Tuesday, August 14, 2007
Endangered killer whales and military vessels that use sonar can co-exist in the straits of Georgia and Juan de Fuca, military experts insist.
However, the navy could probably cope with a mid-frequency sonar ban at certain times of the year, provided Canada is not facing any direct threat, said Capt. Jim Heath, Maritime Forces Pacific assistant chief of staff for operations.
The navy, environmental groups and marine-mammal scientists in B.C. are looking carefully at a ruling from a federal judge in Los Angeles barring the U.S. navy from using high-powered sonar in nearly a dozen training exercises off Southern California.
The judge said lawyers had made a persuasive case that sonar could harm whales and other marine life.
But Heath said Canadian navy sonar is not as powerful that used by U.S. ships, and it is not used if marine mammals are known to be in the area.
"I would think we are excellent environmental stewards. We are very mindful of our impact," Heath said.
Military exercises deliberately avoid places where whales are known to hang out. If marine mammals are spotted, the sonar is shut down, he said. Even if there is no sign of whales, it is ramped up gradually to allow animals that might be there to leave the area.
Many other vessels, from ferries to whale watchers, create noise and use low-power sonar, Heath said. "Look at the amount of marine traffic that travels up and down Juan de Fuca Strait."
The more powerful types of sonar are used to detect submarines or objects such as mines.
It is possible for the navy to train with medium-frequency sonar in open areas, rather than in more enclosed waters, Heath said.
However, the navy's primary role is defence, he emphasized.
"If we perceived ... a real threat, we would have to do whatever we had to do to get the job done."
Cmdr. Rod Hughes, operational readiness officer, said practising in open water, would increase costs and could mean working in rough seas.
"For us to go around the world and do whatever operations we are going to do, we need to practise locally," he said.
Also, the navy is familiar with whale migratory routes inshore, but not as much is known about off-shore behaviour, Hughes said.
The effect of sonar waves on marine mammals depends on how close they are, Hughes said. "Are you standing up close to a rock concert or on a hill a couple of hundred metres away?"
Logically, sonar blasting above a whale is going to be harmful to an animal that relies on acoustics, Hughes said.
But he said the million-dollar questions that, as yet, do not appear to have answers, are: How much does sonar bother whales at a distance? And at what frequencies?
The recently released draft killer-whale recovery strategy, put together for the Department of Fisheries and Oceans by scientists and whale experts, flags military sonar as an element that should be studied in detail over the next two years as teams of scientists come up with action plans to help the killer-whale population recover.
The southern killer whale population, consisting of 87 animals in three pods, is listed as endangered. The northern population, with about 230 members in 16 pods, is listed as threatened.
Numbers have increased marginally over the last decade. But in addition to sonar and noise from boat traffic, the whales are threatened by pollution and shrinking supplies of salmon.
Christianne Wilhelmson, co-ordinator of the environmental group the Georgia Strait Alliance, said she does not believe the navy's mitigation procedures are sufficient to protect the whales.
"They may think there's no marine mammals in the area, but you can't always see them and there may be impacts they're not even aware of."
It's possible the whale-recovery strategy will require a ban on military activity in areas around Vancouver Island at certain times of the year when killer whales are in residence, Wilhelmson said.
"Whale biologists certainly look at this as an issue."
Most of the resident killer whales are around Vancouver Island during the summer and fall, but some, such as J Pod, tend to stay in the area year-round.
The draft recovery strategy says the threat that active sonar may pose "must be considered and precautionary measures should be considered by both navies."
A PRIMER ON SONAR
Sonar is the transmission of sound underwater. Of course, there's more to it than that.
- With active sonar, the sound is put into the water and it bounces back when it hits an object. Both the military and other vessels, from cruise ships to fishing vessels, use active sonar for navigation or for finding fish. The high frequency/low power type, directed straight at the ocean bottom, is believed to have little effect on sea life.
- The military also uses a stronger form of active sonar to locate submarines, mines or other objects. Sound travels farther and is directed out into the water.
- The Canadian navy uses medium frequency/medium to low power for its operational sonar. The U.S. navy, with bigger ships and a bigger budget, uses low frequency/high power, meaning the sound can travel hundreds of kilometres.
- The range in sonar types are analogous to the difference between sitting in the front row of a Rolling Stones concert versus listening to a car stereo, said Cmdr. Rod Hughes, Maritime Forces Pacific operational readiness officer. "We tend to operate car stereos," he said.
- Passive sonar involves the dropping of hydrophones into the water, allowing operators to listen to sounds.
- Whales use their own sonar to locate food and travel underwater. There is scientific evidence showing they can become disoriented by powerful blasts of mid-frequency sonar, sometimes beaching themselves and sometimes surfacing too quickly, giving themselves the marine-mammal equivalent of the bends.
- Mid-frequency sonar exercises conducted by the USS Shoup in Haro Strait in 2003 corresponded to changes in behaviour by J Pod, part of the endangered southern-resident killer whale population. Acoustic trauma arising from the exercises might have contributed to the strandings and deaths of harbour porpoises.
Quelle: Times Colonist (Victoria)
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