|dB = decibels - Sound is measured in units called decibels. Exposure to a continuous sound at or above 85 decibels can damage a human's hearing ability.|
|177 dB||Large Tanker A continuous noise on shipping pathways all over the world|
|183 dB||Icebreaker A cycling noise primarily in Arctic Ocean, north of Canada, Alaska, and Russia|
|195 dB||Supply Ship Continuous sound emitted along shipping lanes all over the world||210 dB||Seismic oil exploration |
Low pitched pulses of sound, generated in oil-rich ocean areas world wide
|167 dB||Dredging boat |
Creates continuous, low frequency grinding, in near shore construction areas
|60/70 dB||Human Conversation From 1 Metre distance|
|90 dB||City Traffic|
Measurements of noise levels in the frequency band 25–50 Hz show an increase of approximately 19dB during the period 1950–2007, corresponding to a rate of increase of 3.3dB per decade. The baseline value of 20 to 52dB (in yellow) is associated with natural/biological noise and is assumed to be constant during this time period. The human component (in red) is associated with commercial shipping noise and was estimated from measurements made in the Northeast Pacific Ocean in 1950, 1965, 1978, 1980, 1986, 2001 and 2007.
Bubbles cavitation is produced in millions by the rotation of the ship's propeller blades in water. which causes any dissolved gas in the sea to change into bubbles (just like when a bottle of tonic water is open and releases the hissing, bubbling gas). Then the bubbles collapse (implode) and generate an intense shock waves which act like a hammer on the blades with a force in excess of 7kg per square centimeters. The ship's propellers generate millions of such cavitation bubbles as can be seen in the wake of ships at sea. These millions of imploding cavitation bubbles are the main source of wear (pitting) on popellers (see image). These cavitation bubbles continuously reverbate in the sea as the ship progresses on its journey! Cavitation certainly has the potential to generate noise that is greater than 10 dB above machinery and other noises and is is the most prevalent source of underwater sound in the ocean - the unmistakable signature of large commercial vessels. There are technologies to suppress the effects of cavitation; used mainly for military and specialist research vessels. However, these are very specialised and often work at the expense of increasing the vessel’s fuel consumption. Hence, such technologies are unlikely to be accepted by the broader commercial shipping industry - tough luck for marine life!
Because sound can travel hundreds or even thousands of miles under water, it’s not surprising that seismic airguns can be heard at great distances. In 2004, bioacousticians began reporting that airgun noise from distant surveys along the coast of South America (and perhaps Africa) can be the dominant sounds in some mid-Atlantic study sites, at times making it difficult or impossible to hear the whales or seaquakes they are trying to study. Airgun noise is over 200dB (often 230db) at the source, drops quickly to under 180dB (usually within 50-500 meters, depending on source level and local conditions), and continues to drop more gradually over the next few kilometers, until leveling off at somewhere near 100dB. At this level, the sound can still travel for hundreds or thousands of kilometers. In many or most locations, 100dB is significantly louder than the existing ambient background noise, so when the airguns raise the background noise to this level, it potentially masks local biological calls and signals. Such effects have been noted at ranges from 1,300 to 3,000 km from active surveys. These sounds are primarily low frequency, so at long distances, the effects are most pronounced for larger species such as the great whales and some fish that use low-frequency sounds. Credit and full text at: http://www.beachapedia.org/Seismic_Surveys
Soon, the Pacific Merchant Shipping Association, which represents marine terminal operators and ocean carriers calling on west coast ports, will announce a large-scale project aimed at reducing ship strikes. Timed to coincide with the lane changes, the initiative will help fund whale monitoring flights over the Channel Islands, integrate and test a whale-spotting app and facilitate the placement of whale observers on ships. The shipping lane changes come as ship strikes are growing in visibility and concern is mounting. In recent years, record numbers of endangered whales have washed ashore or been dragged into ports, wrapped around the bows of ships. But those whales are just a fraction of the total killed -- the ocean doesn't purge its fallen as often as they are taken. "I think it's likely that less than 10 percent of ship strikes are documented," said John Calambokidis, a research biologist with the Cascadia Research Collective, who has been studying ship strikes in the Pacific Ocean for decades. "This is a worldwide problem." With ship densities unlikely to decline any time soon, and whales being difficult to relocate, scientists, conservationists, and the shipping industry are working on ways to minimise the intersections of the seafaring giants.
Full story at: http://www.wired.co.uk/news/archive/2013-06/03/whales-and-shipstrikes/viewgallery/304689
The Navy uses active sonar which propagates sound waves through the water. There are three types of active sonar: low (LFA), mid (MFA) and high frequency active (HFA). MFA and LFA are types of SONAR used by the Navy to locate objects in the water. A loud blast or sound wave is emitted into the ocean and then bounced off of an object. The reflection of the blast, called a "ping", is then listened for to judge the object’s size, distance and sometimes shape. In general, lower frequencies travel longer distances. The “loudness” or amplitude of MFA and LFA sonar is upwards of an astounding 235 dB; the deafening equivalent of a space shuttle at launch. HFA is often used as a deterrent for marine mammals or fish.
A ship’s main engine is a massive structure with an average height of about 3 to 4 storey building (approx. 45 feet) and weight equals to 500 elephants (2,500 tonnes)and, that's not taking into account the shaft and massive propellers. The recognised threshold above which there is a risk of hearing loss is 80 dB(A), 8 hours per day. Noise in engine rooms exceeds 105 dB and is perceptually equivalent to levels found on board merchant ships of any size with sound proofed control cabins. Personel in engine rooms are not, in general, allowed to be exposed to sound levels exceeding 80 dB(A) unless they are wearing the ear muffs provided.
Whales and other marine mammals rely on their hearing for life's most basic functions, such as orientation and communication. Sound is how they find food, find friends, find a mate, and find their way through the world every day. So when a sound thousands of times more powerful than a jet engine fills their ears, the results can be devastating and deadly. This is the reality that whales and other marine mammals face because of human-caused noise in the ocean, whether it's the sound of airguns used in oil exploration, subs and ships emitting sonar or the ever-bigger commercial ship containers and tankers. Manmade sound waves can drown out the noises that marine mammals rely on for their very survival, causing serious injury such as acoustic pressure trauma and even death. Research finally suggest, for example, that Navy sonar may mimic sounds produced by predatory killer whales. That may drive prey like beaked whales away from feeding areas — and send them rocketing to the surface, giving them the equivalent of the bends.