Ocean Noise Pollution Facts
Imagine yourself on a busy street in New York City: Car horns blaring, vendors yelling, planes overhead, jackhammer wailing; you’re inundated with sound. It can be disorienting, frustrating and even painful. Your head pounds, blood pressure increases, and you seek refuge, but there is none. You can close your eyes but not your ears. Marine mammals face these threats every day as their world is polluted with extraneous noises.
Noise intensity is measured in decibels (dB), a “dimensionless” unit much like a percentage (i.e. a glass may be 35% full, yet the volume unknown). For each decibel increase the intensity raises logarithmically, where a 10 dB increase is 10 times louder, while a 20 dB increase is 100 times as loud, etc.
In the marine environment, where light’s reach is limited, sound expression and recognition are paramount to the health and safety of marine mammals. Using sound to communicate, navigate, and to locate food with a mechanism analogous to active SONAR (SOund NAvigation and Ranging) whales maintain a broad variety
of calls for communication and are also capable of using ultrasound to echolocate. Through clicks and sound pulses echolocation helps find prey and predators and is also used to define marine mammals location to other objects in the water. In communicating over long distances whales also use the deep sound channel, a phenomenon that allows long-range sound propagation. Submariners also use the sound channel to propagate sonar over long distances, possibly interfering with whales' communications.
Sources of Noise Pollution:
Noise pollution exists in many forms. The most pervasive contributors of noise pollution in the marine environment are: SONAR, large commercial ships and underwater exploration and mining.
The Navy uses two different classes of SONAR, passive and active: Passive sonar listens for sound waves without emitting any sound, while active sonar propagates sound waves through the water. There are three types of active sonar: low, mid, and high–frequency active (LFA, MFA, 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.
RIMPAC Sonar Exercises
RIMPAC stands for Rim of the Pacific. RIMPAC is an antisubmarine warfare exercise conducted biannually by the U.S. Navy in conjunction with several other nations. The exercise includes the use of mid-frequency active sonar and ordnance detonation. Mid-frequency active range sonar (1 kHz to 10 kHz) is deployed in an area covering 210,000 nautical miles (nm) for 44 different military activities. Roughly 532 hours of acoustic noise could be put into the oceans at a source level that can exceed 235 decibels.
During RIMPAC activities in 2004, a pod of 150-200 melon-
headed whales mass stranded in Hanalei Bay, resulting in one calf dying. The National Oceanic and Atmospheric Administration (NOAA) admitted that it is “highly
plausible” that RIMPAC was the cause of this stranding. Pacific Whale Foundation is concerned that the Navy’s standard operating procedures and protective measures are inadequate when dealing with the varying dive times in the Hawaii Range Complex. Trained lookouts will not see marine mammals in time or at night and not enough is known about sonar’s effects on marine mammals to modify an exercise effectively around marine mammal behavioral patterns.