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Acoustic impacts on marine life A growing body of evidence confirms that intense sound produced by human-generated noise in the marine environment can induce a range of adverse effects on marine mammals and other marine organisms. These effects include death and serious injury caused by hemorrhages or other tissue trauma; stranding; temporary and permanent hearing loss or impairment; displacement from preferred habitat; and disruption of feeding, breeding, nursing, communication, sensing, and other behaviors vital to survival. Recent studies show that ocean background noise levels have doubled every decade since the 1940s in some areas. The primary sources of human-produced noise in the marine environment are shipping, air guns used for oil and gas exploration under the ocean floor, and military sonars. As a result of the masking effects of human-produced ocean noise pollution, the possible communication range of blue whales has decreased from greater than one thousand kilometers to only one hundred kilometers in the noisy Northern Hemisphere. We do not know how this affects the ability of this endangered species to find food and mates. Mass stranding of whales increased dramatically after 1961, when more powerful naval sonars began to be used (Friedman). In the recent past marine mammal strandings have occurred in Greece (1996), the Bahamas (2000), Madeira (2000), Vieques (1998, 2002), the Canary Islands (2002, 2004), the northwest coast of the United States (2003), and Hawaii (2004). Each stranding has been correlated with the use of high-intensity military sonar. These sonars—both low-frequency (LFAS) and mid-frequency sonar—can have a source level of 240 decibels, which is 1 trillion times louder than the sounds whales have been shown to avoid. One scientist analyzing underwater acoustic data reported that a single low-frequency sonar signal deployed off the coast of California could be heard over the entire North Pacific Ocean. Necropsies performed on whales stranded in the Bahamas (2000) and the Canary Islands (2002) revealed hemorrhaging around the brain and in other organs, most likely due to acoustic trauma from the use of high-intensity sonar. It appears that the sonar exercise in the Bahamas in 2000 may have either killed the entire population of beaked whales in the area or caused them to permanently move away (Balcomb and Claridge ). In December 2004, 169 whales and dolphins died on beaches in Australia and New Zealand after reported military exercises and air gun use in the area. A report commissioned by the U.S. Navy stated that “the evidence of sonar causation [of whales stranding] is, in our opinion, completely convincing” (Levine et al.). The global magnitude of the problem has not been determined because many fatally injured animals sink in the deep ocean, and not all injured whales strand onto beaches where they can be found. Intense noise generated by commercial air guns used for oil and gas exploration and oceanographic experiments, underwater explosives, and ship traffic also pose a threat to marine life. Air gun use was correlated with whale strandings in the Gulf of California and Brazil in 2002. High-intensity sonars and air guns not only impact marine mammals but also have been shown to affect fishes, giant squids, and snow crabs. In a study by the British Defense Research Agency, exposure to sonar signals caused auditory damage, internal injuries, eye hemorrhaging , and mortality in commercially caught fishes. Air guns caused extensive damage to the inner ears of fishes and lowered trawl catch rates 45 to 70 percent over a 2,000-square-mile area of ocean (Norwegian Institute of Marine Research). Catch rates did not recover in the five days surveyed after air gun use stopped. This presents the possibility that increasing production of intense underwater noise can significantly and adversely impact already depleted fish stocks in the ocean, the food supply, employment, and the economies of maritime countries. In his 2005 report to the General Assembly, the secretary general of the United Nations listed underwater noise as one of the current major threats to some populations of whales and other cetaceans. He called for better assessment of the impact of underwater noise on Green / Acoustic Impacts on Marine Life | 39 40 | minett / cephalopods and decapod crustaceans fishes and cetaceans as well as consideration of noise abatement strategies. Related articles: Animals used in research; The complexity of animal awareness; The declaration of the rights of cetaceans; Intelligence in whales and dolphins; Marine mammals in captivity; Sea fishes and commercial fishing; Stranded marine mammals Balcomb, K. C., and Claridge...

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