Acoustic Impacts

June-July 2005

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by Marsha L. Green

In the past decade, 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 US (2003) and Hawaii (2004). Each stranding has been correlated with the use of high intensity military sonar. These sonars—both low frequency and mid frequency—can have a source level up to 240 db, which is one 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 and the Canary Islands 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 may have decimated the entire population of beaked whales in the area. In December 2004, 169 whales and dolphins died on beaches in Australia and New Zealand after military exercises and air gun use in the area.

In January 2005, 37 whales stranded on the US coast of North Carolina after high intensity sonar was used in a naval exercise. In March, 2005 almost 80 dolphins stranded on the US coast in Florida after the use of naval sonar. Though still too recent to link definitively to sonar, these last three strandings have triggered official inquiries.

Intense noise generated by commercial air guns used for oil and gas exploration and oceanographic experiments, underwater explosives, and shipping 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. The global magnitude of the problem has not even been determined, as many fatally injured animals are likely to sink in the deep ocean, and not all injured whales strand.

The effects include death and serious injury caused by hemorrhages or other tissue trauma, strandings, 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.

High intensity sonars and air guns affect not only marine mammals but also have been shown to impact fish, giant squid 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 fish. Air guns caused extensive damage to the inner ears of fish and lowered trawl catch rates 45–70% 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 disrupt food supply, employment and the economies of maritime countries.

Recent studies show that ocean background noise levels have doubled every decade for the past six decades. 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 1,000 km to only 100 km in the noisy Northern Hemisphere. We don’t yet know how this affects their ability to find food and mates.

The North American Ocean Noise Coalition (NAONC)

The North American Ocean Noise Coalition is a group of conservation and animal welfare organizations in North America that are concerned about the ocean noise issue, including the NRDC, Animal Welfare Institute, Humane Society, Earth Island Institute, Seaflow, Ocean Mammal Institute, and the Acoustic Ecology Institute. The coalition works with the European Coalition for Silent Oceans (which has about 54 member organizations) and is headed by OceanCare in Switzerland. Elsa Cabrera in Chile has recently organized a coalition in Latin America. This global approach is especially important at the UN. For updates see www.oceanmammalinst.org and http://www.earthisland.org.

The Oil Free Coast

The Oil Free Coast is a Canadian coalition of scientists, environmental groups and fisheries organizations in BC, is critical of the Dept. of Fisheries and Oceans’ draft Statement of Canadian practice on the Mitigation of Seismic Noise. “The Statement of Canadian Practice makes claims that are scientifically indefensible and irresponsible given our current knowledge,” says Dalhousie University whale researcher Dr. Lindy Weilgart. “It makes a mockery of science-based stewardship and fails to adequately protect the marine environment.” The Oil Free Coast coalition, made up of 105 organizations, is calling on Fisheries and Oceans Canada to abandon its draft Statement and initiate an independent evaluation of the impacts of seismic testing. See www.oilfreecoast.org.

© Marsha L. Green, PhD, info@oceanmammalinst.org.