AMERICA鈥橲 search for as yet undiscovered oil and gas supplies could have a serious impact on its marine life. Acoustic surveys used to look for energy deposits under the ocean floor could injure or scare whales and dolphins, and potentially harm fish and invertebrates too, ecologists warn.
The US Energy Policy Act, passed by Congress this month, includes a provision for the seismic mapping of the country鈥檚 entire outer continental shelf 鈥� defined by the government as the area of coast that stretches from the far edge of state waters some 5 to 19 kilometres offshore to the far edge of national waters some 320 kilometres out to sea. Boats would fire loud blasts of sound at the ocean floor, then use hydrophones to record the sounds reflected back, mapping the contours of the continental shelf to help them pinpoint oil and gas reserves.
But this region of coast contains highly productive biodiversity hotspots, such as the Georges Bank fishing ground off Cape Cod in the Atlantic, says Damon Gannon of the Mote Marine Laboratory in Sarasota, Florida. He and other biologists say the noise produced by large-scale seismic surveys could chase whales from breeding or feeding grounds, or make it difficult for dolphins to hear the sonar they use to catch fish.
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For example, the endangered North Atlantic right whale spends much of its life in shallow waters near Cape Cod and has a calving ground off Georgia and Florida. It is not known how right whales respond to such acoustic surveys, says marine biologist Linda Weilgart of Dalhousie University in Halifax, Canada, but their closest living relative, the bowhead whale, avoids areas that are being seismically mapped in the Arctic. 鈥淪eismic profiling has been linked to all sorts of displacement of whales from critical habitats,鈥� she says.
鈥淪eismic profiling has been linked to the displacement of whales from critical habitats鈥�
The air-gun arrays used to map the sea floor produce 230 to 240 decibels in water, comparable to the noise made by navy sonars, which have been implicated in strandings of beaked whales.
Whether the acoustic surveys will have any effect on fish and marine invertebrates is unclear. Norwegian researchers have found that fewer fish are caught on long lines for days after an air-gun array has been fired, but the number of fish caught in nets does not change. There is some evidence the noise damages the ears of some fish species but not others, while its effects on clams, lobsters and crabs are not known. Last year, Angel Guerra of the Institute for Marine Investigations in Vigo, Spain, blamed seismic tests for the strandings of several giant squid with damaged ears along the Spanish coast.
