Water column pressures induced by vibrators operating on floating ice

Abstract

Over the past 30 years, there has been an increased interest in the effects of anthropomorphically generated noise on the hearing of marine animals. In response to this concern, and to promote the conservation of marine environments, the U.S. Congress passed the Marine Mammal Protection Act (MMPA) in 1972. In essence, this act made it illegal to intentionally harass or harm any marine mammal. Because sound propagating through water has the potential to disrupt behavior patterns or impair the hearing of different species, several government regulatory agencies such as the National Marine Fisheries Service, the Fish and Wildlife Service, and the Minerals Management Service have developed programs to study these issues. Of particular concern are pressure waves generated by marine seismic air-gun arrays. It is feared that these high pressures may cause a temporary or permanent threshold shift in the hearing of certain marine mammals. To avoid this possibility, government regulatory agencies require a series of acoustic studies prior to seismic operations in offshore areas of the State of Alaska. This information is used to establish a safety radius for certain marine mammals. If an animal is observed to swim within this radius, the seismic vessel must stop operations. The MMPA does not specifically address the issue of harassment or harm to fish populations. Nevertheless, several federal, state, and local government agencies, as well as stakeholders, have expressed increasing concern over the effects of seismic noise on fish. The concerns are much the same as they are for marine mammals. Government biologists want to know if the sound levels produced by seismic sources have the potential to harm or kill local populations of fish. Actually these questions have been addressed many times over the last several years. Several studies have shown that air guns do not produce an acoustic field …