Ocean Noise Pollution and its Harmful Affects on Aquatic Mammals
This topic submitted by Allison Carlascio (
Carlasal@muohio.edu) at 9:45 PM on 6/5/07.
Divers chase a sea turtle at the wall break,
12 m deep, San Salvador, Bahamas.
While terrestrial pollution has always taken the forefront of concern, underwater noise pollution is a disturbing problem that is quickly degrading the ocean life that we know and love. With a growing use for underwater acoustics, and both man-made and natural noise sources, underwater noise pollution has been proven to have severely damaging affects to the ocean and all the inhabitants in it, especially aquatic mammals. I will not only discuss the sources that are contributing to these severe physiological and behavioral problems but I’ll also discuss these problems themselves to a certain extent. I will also take an inward look at recent news that has impacted people’s understanding of the severity of this noise, and discuss some preventative actions to hopefully reverse the detrimental damage that has already been done.
Ocean noise pollution can be described many ways. In simple words, the ocean is filled to the brim with loud noises. Over time this noise has increased a tremendous amount. In fact, since 1970 it is estimated that noise solely from human activity has increased at 10 decibels per decade. (Darlene) This “human activity” comes from various sources that exude different harmful noises. Some examples of this are military sonar, used for defensive and research purposes, fishing boats, merchant ships, research vessels, and oil rigs. (McCarthy) Other forms are pingers that are used to locate flight recorders by airlines, sidescan sonars that locate shipwrecks, multibeam sonars that create a special 3D floor-plan of the ocean floor, and many more. (McCarthy)
Both sonic noise and seismic surveys are used in the efforts of evolving research on effects of this sound on the oceanic environment. Sonar noises, such ones used in Naval weaponry, are meant to be heard over vast distances but short sequence periods. Seismic surveys, such ones used in exploration of oil and geological studies, are very similar in intensity to short military sonar, but they are more deadly because they are set for weeks or even months. (Cummings) When speaking of seismic activity, the sound impulses are produced by ejecting bubbles of air. Airguns, a source of this seismic noise, expel 30 to 800 cubic inches of air per shot. They are like air cannons and are either used singularly or collectively to create one massive sound that uses up to 8080 cubic inches of air per shot. (Cummings) These seismic surveys are being used all over the world, in places such as the continental shelves, which is the most common region, as well as the North Sea, Gulf of Mexico, and areas around Australia, Venezuela, Brazil, and Alaska. (Cummings)
Even though sonic and seismic noises are two deathly leading causes for concern when noise pollution is considered, there are many other sources that can be almost as detrimental. Natural sources of high intensity sound, such as wave action, sea quakes, heavy rain and whale vocalizations, can be even lower frequencies than seismic arrays and therefore more disruptive. (Cummings) Overall ambience has also increased about 10-20 dB over the past 100 years. Another way to categorize ocean noise pollution is labeling pollution as either acute or diffuse. Acute pollution which is equivalent to the sonar noise tests described previously, or diffuse pollution which is a generalized background noise that affects a larger region. (Pavan) An example of this diffuse pollution is ship traffic. (Pavan)
Even though there are differences between all of these sources of noise, they all contribute to the ever-increasing pollution in the waters. This noise affects marine mammals in almost every aspect of their life. In order to communicate with each other, many species of whales depend on hearing calls from other whales. These calls can easily be hidden behind “acoustic masking” from sounds in the same frequency ranges. (Cummings) The calls of baleen whales (humpback, blue, fin, and grey whales) are frequencies that range from 20 to 500 Hz. (Cummings) This shows that the frequencies of sonar and even natural sources can easily mask the sound of the calls of whales and other marine mammals and significantly alter their natural behaviors.
This noise can also mask other behaviors such as dolphins’ special echolocation skills used for navigational purposes, foraging for food, and communication within the specific group members. To understand the excessive impact noise pollution has on the marine wildlife, it is pertinent to acquire knowledge on these behaviors.
To locate food, many marine mammals send out high intensity pulsed sounds that reflect back after it strikes an object. (Discovery of Sound) The sounds that come back to the animal are very different from the sent out sound. This is because the returning sound relays information about the size, shape, direction, speed, and orientation of the prey. (Discovery of Sound) Certain species such as bottlenose dolphins have individual, specific vocalizations that are used for communication between the members of their group they migrate with. In fact, each individual dolphin has their own significant whistle that is recognized throughout the group. (Discovery of Sound) The sperm whale produces their vocalizations between feeding sessions when they are socializing as a group at the surface, but instead of whistles, they produce clicks called codas. (Discovery of Sound)
Vocalizations are also used in the context of reproduction and aggression. In reproduction, the males compete with other males for access to females and they do this by producing detectable vocalizations. (Discovery of Sound) Also, females can compare these sounds to see which male she would like to mate with. During the breeding season, the ocean is full of humpback whale songs. These songs are vocalizations that are oftentimes sung for long periods of time. (Discovery of Sound) Aggression is another behavior that is directly related to auditory and vocalization systems. There are either sounds to declare a “readiness to fight” or to ward off predators. (Discovery of Sound)
The increasing noise in the ocean has crucially affected these behaviors and there are many cases from different species that prove this. Californian sea lions use sonar to communicate with each other and echolocate, and with this ocean noise pollution it makes it extremely difficult to complete these tasks. (Causes of Ocean Noise Pollution…) The gray whale similarly suffers from this noise when they break away from their normal migration routes, have trouble with finding food, or can’t properly communicate. (Causes of Ocean Noise Pollution…)
Another affect of this noise is physiological damage. This noise pollution impairs and interferes with proper functioning of marine mammals’ acoustic perceptual system. There are known cases of beached whales and dolphins that show not only long-term hearing loss, but definite tissue damage such as hemorrhaging in their ears, and lesions caused by bubble formation and expansion in the tissues. Other proven signals that this noise is causing damage in marine mammals is increased stress, avoidance and change of swimming patterns according to where the sound is generated from. (Cummings)
The sense of hearing is, in fact, the most important sense for these marine mammals and it is evident by the extensively evolved ear and neural auditory center. (Darlene) Not only do they have more neurons dedicated for this hearing, but the dominant temporal lobes (which control the auditory system) show they have quicker auditory and signal processing capacities compared to other mammals. (Darlene) Sublethal impacts are deathly harmful to the auditory system because this noise greatly exceeds the ear’s tolerance, and is consequentially very damaging to the ear over an extended amount of time. (Darlene) A threshold shift is a loss of sensitivity caused from this noise, and there are two kinds differing with severity. A recoverable threshold shift is where the inner ear isn’t greatly damaged, and a permanent threshold shift is damage to the ear and hearing that will never improve. (Darlene)
Even though there are many laws and acts established by different nations’ governments, it is obviously not enough protection because the problem of ocean noise is slowly but surely increasing. Some countries have taken initiative in trying to “take the bull by the horn” and decreasing seismic surveys near marine parks, such as Australian and Bermudian governments. (Cummings) Other policies such as The Acoustic Risk Mitigation Policies are aimed in finding specific areas and periods for potentially harmful situations that minimize the effects to the organisms. (Pavan) In 1982, the United Nations Convention on Law of Sea provided provisions related to marine environment protection and prevention of this marine pollution. (McCarthy) Even though there has been an increasing amount of laws that help prevent against sonar noise, there are still no international treaties or laws that address operations of sonar’s or transmission of sound. (McCarthy)
There are many instances that prove the harmful affect of sonic and seismic noise. On March 13, 2000, 17 whales of four different species were found on the beach at the same time that the US Navy was conducting acoustic antisubmarine activities in the area. (McCarthy) Because of these occurrences, there was a press conference held in Washington DC that concluded to exclude active acoustic sources. (McCarthy) The International Whaling Commission has a significant role in ocean noise pollution and the protection of whales. They suggest that “vessel operators should be aware of acoustic characteristics of their target species and of their vessel” and that “the vessel design should minimize the risk of injury and to avoid sudden changes in speed, direction or noise.” (McCarthy)
Other forms of protection would be creating special regions for specific species that are reserved by law and protected so that these species can live unharmed. There are known “whale sanctuaries” in Southern Africa, Australia, and the US. (McCarthy) This would be a good idea in regards to wildlife that are extremely sensitive to this pollution and greatly affected by its impacts. Another good idea would be to regulate this concerning issue by environmental protection instead of individual countries trying to enforce separate laws for the ocean in their region.
There are so many inventive ways that are beginning to roll into the picture to prevent the ocean life from being fatally destroyed. With this increasing noise level, marine mammals can’t function properly, which affect their prey, which indirectly and directly affects us. When one part of this ecosystem changes drastically, the whole puzzle of the ocean doesn’t work, which is detrimental for the entire world. For this reason we must take a dedicated look at the problem, share the knowledge with many, and research what we can do to prevent our beautiful ocean from changing forever.
Causes of Oceanic Noise Pollution and Recommendations for Reduction. Oceanlink. http://oceanlink.island.net/oceanmatters/noise%20pollution.html
Cummings, Jim. Brandon, Natalie. SONIC IMPACT: A Precautionary Assessment of Noise Pollution from Ocean Seismic Surveys. Acoustic Ecology Institute. Greenpeace USA. June 2004.
Darlene R. Ketten, Ph. D. Marine Mammal Auditory Systems: A Summary of Audiometric and Anatomical Data and its Implications for Underwater Acoustic Impacts. Woods Hole Oceanographic Institution Harvard Medical School. http://www.solcomhouse.com/auditory.htm
Discovery of Sound in the Sea. University of Rhode Island. Office of Marine Programs. http://www.dosits.org/animals/use/2a.htm
McCarthy, Elena M. International Regulation of Underwater Sound. University of Rhode Island. Kingston, RI. 2000.
Pavan, Gianni. Effects of Underwater Noise on Marine Mammals. Universita degli Studi di Pavia.August 2006. http://www.unipv.it/webcib/edu_noise_uk.html.
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