Increasing levels of ocean noise generated by military sonar, shipping, and oil and gas exploration is threatening dolphins and whales that rely on sound for mating, finding food and avoiding predators, according to a new report.
The report released Monday by the Natural Resources Defense Council found that the affects of ocean noise on marine life range from long-term behavioral change to hearing loss to death.
The report, a follow-up to a 1999 study, included details from necropsies performed on beached whales suspected of being exposed to Navy sonar.
Scientists who examined more than a dozen whales that beached in the Canary Islands in September 2002 found bleeding around the brain and ears and lesions in the animals' livers and kidneys.
"It is a set of symptoms that have never before been seen in marine mammals," said Michael Jasny, the report's principal author. "That physical evidence has led scientists to understand that the sonar is injuring the whales in addition to causing them to strand."
Researchers believe that whales are suffering the same type of decompression sickness that is known as "the bends" in humans. The leading theory is that sonar either causes whales to panic and surface too quickly or forces them deeper before they can expel nitrogen, leading to nitrogen bubbles in the blood.
A federal probe into the mass stranding of 17 whales in the Bahamas in March 2000 cited the Navy's use of mid-frequency sonar as a contributing factor.
The Natural Resources Defense Council sued the Navy last month in federal court in Los Angeles in an attempt to curb its use of mid-frequency sonar, which is the most common method of detecting enemy submarines. The environmental group wants limits on sonar during training exercises, not in war.
In the new report, the NRDC urged the National Marine Fisheries Service to better enforce the federal Marine Mammal Protection Act. The service should also require the Navy to obtain permits for its sonar exercises, according to the report.
A fisheries service spokeswoman said the agency had not seen the report and could not comment on it.
Jasny said noises from oil and gas exploration have also been linked to lower catch rates of halibut, cod and other species of fish.
"It's been shown that some species of fish suffer severe injury to their inner ears, which can seriously compromise their ability to survive," he said.
The NRDC recommended year-round restrictions of excessive ocean noise in critical habitats and seasonal restrictions on migration routes. For example, the group suggested that oil-and-gas companies avoid seismic surveys in the winter off the west coast of Africa when baleen whales are breeding offshore.
It also called on the fisheries service to increase oversight of oil and gas surveys, which rely on shooting high-intensity air guns at the ocean's floor.
The true impact of ocean noise remains unknown because strandings likely represent just a small portion of marine life effected by excessive noise, Jasny said.