A humpback whale (Megaptera novaeangliae), one of the many cetaceans relying on sound across vast distances.
Credit: Louis Herman/NOAA
There is mounting evidence that noise can cause sea life to change behaviour. Canadian scientists have shown that killer whales are deterred by 'acoustic harassment' - loud alarms set off to keep them away from salmon farms. Californian researchers found that low-frequency sound can change the diving behaviour of elephant seals. And a U.S. Navy study shows that humpback whales change their song when obliged to compete with military low-frequency sonar.
But research into floating hotels on the Great Barrier Reef suggests some sounds may actually attract sea larvae - and hence the larger fish and animals that feed on them, says McCauley. Amusingly, fish also seem better able to regulate their noise emissions than people: his early research revealed that the deafening choruses of certain fish on the Barrier Reef were timed or located in such a way as not to interfere with the singing of other sea species. Ocean noise pollution is a rising issue in environmental and conservation circles. The seminal report, Sounding the Depths: Supertankers, Sonar and the Rise of Undersea Noise, was published in New York in 1999 by the Natural Resources Defence Council.
However before this came a number of fiery spats, including a rather unedifying one between physicists and biologists over a global experiment in transmitting acoustic waves through the deep ocean as a way of measuring global warming, known as ATOC (Acoustic Thermometry of Ocean Climate). The physicists argued their low-frequency sound waves were harmless; the marine biologists contended they would interfere with one of the main communication channels used by whales, in effect scrambling their long-distance conversations.
Scenting another rising environmental issue, green groups have been quick to take up the cause of ocean noise. At its meeting in Bangkok, Thailand in November 2004, the World Conservation Union adopted a resolution that declared noise was a form of ocean pollution. That same month, a U.N. Environment Program meeting of 16 countries formed to protect whales and dolphins in the Mediterranean, Black Sea and Atlantic adopted a resolution acknowledging manmade ocean noise as "a dangerous pollutant which can disturb, injure and even kill whales and other marine species." Groups have sprung up, like the North American Ocean Noise Coalition and the European Coalition for Silent Oceans (ECSO), which are all are calling for sea sanctuaries where all human activity is banned.
Whether sound can cause whale or fish deaths at sea remains debatable. The Whale and Dolphin Conservation Society report says "evidence of the lethal nature of noise for marine mammals comes from recent strandings associated with the use of military sonar, such as the mass stranding of beaked whales in the Bahamas in March 2000".
The ECSO adds "a series of mass mortalities of cetaceans [was] associated with the use of mid-frequency active sonar in coastal environments." It said the best-documented cases were in the Bahamas in the Caribbean and Madeira off the southwestern coast of Portugal in 2000, and the Canary Islands off the coast of North Africa in 2002. Other incidents have occurred in Greece in 1996, the U.S. Virgin Islands in 1998 and 1999, the Canary Islands again - in 1985, 1986 and 1989 - and, most recently, the northwest coast of the United States in 2003. "However, the magnitude of the problem is not known as evidence indicates whales may die at sea where carcasses sink," the report stated. "The proliferation of active sonar poses a threat to already depleted fish stocks throughout the world's oceans."
