The U.S. Navy is looking into whether the activities of a submarine using sonar off the Keys may have played a part in a massive dolphin stranding this week off Marathon.
KEY WEST – The U.S. Navy is investigating whether sonar used in the training activities of a submarine off the Florida Keys this week may have contributed to the mass stranding of more than 80 deep- water dolphins, at least 19 of which have died.
Groups of rough-toothed dolphins mysteriously began beaching off Marathon on Wednesday afternoon — within 24 hours, and perhaps less, of exercises conducted off Key West by the USS Philadelphia, a submarine based in Connecticut.
A Navy spokeswoman said Friday she did not know if the sub was still in the area the day of the stranding or if the vessel was using active sonar — considered by some scientists to be potentially harmful to marine mammals — during its mission.
”This is absolutely high priority. We are looking into this. We want to be good stewards of the environment and anytime there are strandings of marine mammals, we look into the operations and locations of any ships that might have been operating in that area,” said Lt. Cdr. Jensin Sommer, spokeswoman for Naval Submarine Forces, based in Virginia.
There’s a growing body of evidence that active sonar sound waves may harm marine mammals such as dolphins and whales, injuring them in the ears and around the brain, disorienting them, and prompting them in some cases to strand. Marine mammals use sound for just about everything, from feeding to navigating to finding a mate.
Scientists surmise that sonars may disorient or scare the marine mammals, causing them to surface too quickly and creating the equivalent of what divers know as the bends — when nitrogen is formed in tissue by sudden decompression, leading to hemorrhaging.
After a whale stranding in 2000 in the Bahamas, the Navy acknowledged in a report some marine mammal sensitivity to sonars, but has also argued at times that the extent of any cause-and-effect is scientifically vague.
Active sonar allows submarines and ships to spot targets and other vessels by emitting sound waves that bounce off objects, revealing distance and location.
Necropsies already underway on the dead dolphins in Marathon may shed some light on whether the animals suffered any damage to acoustic brain tissue, a potentially key indicator of sonar damage. But test results could take months.
NOTHING RULED OUT
”It’s fair to say we will be looking at any potential contributing factors, and that’s everything,” said Laura Engleby, a biologist with NOAA Fisheries, which is coordinating the stranding response. “We aren’t ruling anything out.”
The Natural Resources Defense Council, a nonprofit environmental group, successfully sued the military in 2002 to limit use of new, low-frequency sonar believed by some to be particularly damaging because of its ability to travel extremely long distances. Some types of sonar can be extremely loud — as much as 235 decibels at close quarters, equivalent to the noise made by a rocket on takeoff – – according to the council.
”Whenever naval exercises coincide with a mass stranding of marine mammals, the government has a responsibility to investigate the connection. We call on them to do that now,” Michael Jasny, a senior policy consultant with the council, said Friday.
SOME RETURN TO SEA
About 20 of the initial group of stranded Keys dolphins made their way back to sea by early Thursday, while 14 were euthanized Friday because of their poor condition. More than 30 others remained in care of biologists and volunteers in a makeshift pen late Friday, from where they were expected to be transferred to rehabilitation facilities.
Whale and dolphin strandings are not uncommon in Florida and elsewhere. Various factors have been blamed — from a few sick animals luring an entire pod toward land, to pollution and algae blooms.
But renewed attention has been focused lately on sonar as a potential cause.
”The more we look now, the more incidents we see,” Jasny said. ”In recent years attention has been increasingly paid to the effect sonar is having on other species” besides whales. “We are only beginning to understand the impact.”
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