Increasing levels of ocean noise generated by military sonar, shipping, and oil and gas exploration are threatening dolphins and whales that rely on sound for mating, finding food and avoiding predators, according to a new report.
The report 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.
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.
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, the AP reports.