It is a well-documented fact that chronic and excessive noise exposure is harmful to our hearing and overall health.
But the bad news doesn't stop here. More and more evidence suggests that noise pollution is not only toxic to us humans, but it also adversely impacts dolphins, whales and other marine mammals, collectively called "cetaceans."
In fact, noise can be deadly to most species living under water.
A cacophony of sound
The aquatic environment is noisy. Heavy rain, volcanic activity, whale songs, toadfish calls, and other sounds emanating from the sea can be so loud as to be audible to a human ear. In fact, according to a recent New York Times article, the underwater reverberates with "fish barks, chatter, groans, drones and cries." A tiny striped cusk eel, the article states, "can sound like a jackhammer."
These sounds, however, are not harmful to sea animals because they are "bio-acoustic," that is, part of their natural environment. As a matter of fact, these creatures rely on the cacophony of undersea sounds to communicate, attract mates, and express fear or distress, especially when predators are lurking in the vicinity. 
Underwater noise pollution found to be harmful to sea animals
The noise becomes problematic - and highly hazardous - when it is man-made. In the past several years many studies have shown that human-produced ocean noise emanating from such sources as military sonar equipment, ship traffic, and underwater drilling, among others, causes hemorrhage or other trauma to the marine mammals' auditory system, sometimes leading to permanent hearing loss, and, indirectly, death. It also causes displacement from their natural habitat, disruption of feeding, breeding, nursing, and other behaviors vital to the species' survival.
In a way, you might say that noise pollution seriously disrupts the sea animals' circle of life.
Breaking the (sound) waves
A growing body of evidence shows that man-generated ocean noise levels have doubled every decade for the past 60 years, posing serious threat to sea animals.
In 2002, seven dead whales were found on a Bahamas beach. They were found to have inner-ear damage, which scientists said might have impacted their sense of direction and ability to navigate.
Since these beached whales were discovered near a U.S. Navy sonar operation, suspicion was directed at the high-intensity sonar equipment, which emits intense waves of sounds across tens and even hundreds of miles of ocean.
Being stranded on land can be fatal to cetaceans, because they get dehydrated and eventually choke to death.
Two years later, 200 melon-headed whales, apparently disoriented by the noise from the Navy maneuvers in nearby waters, stranded themselves in Hanalei Bay, Hawaii.
In January 2005, 37 whales were stranded on a beach in North Carolina soon after sonar was used in a naval exercise. Three months later, 80 dolphins were found on a Florida beach, again right after the use of naval sonar.
In all, in the past two decades, hundreds of stranded sea animals have been discovered on beaches worldwide. All of these instances have been correlated with sonar machinery.
In one case, a specialized team performed CT scans of the beached beaked whales' heads, and noticed auditory damage. X-rays also revealed bleeding around the inner ears, brains and lungs, with trauma to other tissue as well. Scientists say these findings provided the first clear link to naval sonar.
In 2004, the International Whaling Commission's Scientific Committee noted the existence of "compelling evidence" to suggest that military sonar has an impact on beaked whales. Even a U.S. Navy-commissioned report admitted that existing proof of sonar-caused whale beaching is "totally convincing."
The sonar equipment, however, is not the only culprit, and sea mammals not the only victims of man-made noise pollution.
All creatures big and small
Water's density transmits sound more effectively than air. That means that fish, crabs, squid, sea turtles and all the other creatures that live under the ocean's surface are adversely impacted by the noise.
Various studies show that intense noise from boating, air guns, oil drilling and other human-generated ocean sounds poses serious risks to underwater life.
Researchers at University of Kentucky's School of Biological Sciences investigated the effect of boat engine noise on the fish. They played back noise generated from a small, 55-horsepower outboard motor, while measuring auditory thresholds using the auditory brainstem response technique, a method used by many laboratories around the world to investigate auditory sensitivity of fishes. The study's findings demonstrated that even a short exposure to noise causes significant changes in this species' hearing capability.
With such well-documented evidence of damage wreaked by noise pollution, what is being done to protect the ocean wildlife?
Help is on the way
Despite the enormity of the problem, conservation and animal rights groups are making some strides forward toward controlling man-made underwater noise.
"There are many things we can do to decrease ocean noise," OceanLink, an organization dedicated to ocean education, says on its website. "The first would be to simply recognize that there is a noise problem in the oceans, which some governments have begun to do. With formal recognition, it may be possible for national and international agencies to work together to help reduce this problem... For any new policies regarding ocean noise, scientists should follow the precautionary principal to ensure that no further harm will come to marine mammals. From this perspective, governments should adopt legislation with the habitats of marine mammals in mind, ensuring that important areas would receive the least impact possible."
In the United States, Natural Resources Defense Council (NRDC) has been successful, along with other ocean advocacy groups, in pushing for stricter control of two major types of military sonar. Early this year, a federal court banned the Navy from conducting major mid-frequency sonar exercises in California without safety measures in place and rejected a White House bid to excuse the Navy from following the law. At the same time, federal courts also limited the regions where low-frequency sonar may be used and deemed certain species-rich areas, such as the Galapagos Islands and the Great Barrier Reef, off-limits.
"NRDC's goal is to encourage the military to use sonar responsibly, not to stop its use altogether," the organization notes on its website. "Necessary safety measures include putting rich marine mammal habitat off-limits;avoiding migration routes and feeding or breeding areas when marine mammals are present;and turning off active sonar when marine mammals and endangered species are spotted nearby."
While these measures may come too late for hundreds of sea animals that have already been damaged by underwater noise, with the right and concerted action, the seas may resonate with the sounds of whale songs, not the human-produced lethal noises of engines and machinery.
"Reprinted with permission from the leading internet source on hearing loss and hearing aids, Healthy Hearing - www.healthyhearing.com. Originally published August 11, 2008."
Man-Made Noise is Harmful to Sea Animals
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