Protection from, and mitigation of, the potential effects of seismic exploration on marine mammals

Abstract

In recent decades, concern has arisen that sounds introduced into the ocean by humans could have adverse effects on marine mammals. Sound is transmitted very efficiently through water, and underwater sound can often be detected many kilometres from the source. This efficiency of underwater sound propagation has also allowed marine mammals to use underwater sounds as a primary method of communicating and exploring their environment. In the United States (US), these concerns have contributed to the enactment and expanded application of the Marine Mammal Protection Act (MMPA) of 1972, and other laws and regulations and have generated research on the effects of man-made noise on marine mammals (Richardson et al. 1995). Much of the research on this problem to date has focused on the behavioural responsiveness of marine mammals to underwater sound. The US Minerals Management Service (MMS) has funded many of the studies related to the effects of seismic survey noise, especially on bowhead whales (Balaena mysticetus) in Alaska and grey whales (Eschrichtius robustus) off the central California coast. Although the effects of low-frequency sound on marine mammals have increasingly become the focus of research, much uncertainty remains. In 1992, the US National Research Council (NRC) formed a Committee on Low- Frequency Sound and Marine Mammals to review current knowledge on the subject and identify research needs (NRC 1994). In its 1994 report, the Committee concluded that the existing data were extremely limited and could not constitute the basis for informed prediction or evaluation of the effects of intense low-frequency sounds on any marine species.