Abstract

The intense sounds produced during seismic surveys may potentially have physical, physiological and behavioural effects on marine mammals. In addition, there may be longterm consequences due to chronic exposure, and sound could affect marine mammals indirectly by changing the accessibility of their prey species. The most likely physical/physiological effects are thought to be shifts in hearing thresholds and auditory damage. No studies have attempted to measure this directly but there are indications that, for sensitive species at least, this may occur at short to moderate ranges. Behavioural responses, including fright, avoidance and changes in behaviour and vocal behaviour, have been observed in baleen whales, odontocetes and pinnipeds; in some cases at range of tens or hundreds of kilometres. The biological significance of these known or predicted effects has not been measured. However, biologically plausible scenarios can be constructed which indicate that in cases, where feeding, migration and social behaviour are affected, populations could also be reduced. Marine mammals may face particular problems when many seismic surveys occur in a region at the same time as happens in areas of high interest, such as the Atlantic Frontier. This review highlights the large gaps that exist in our understanding of all aspects of this potential problem. Even the nature of the seismic signature itself at different ranges and depths is poorly understood, and there may often be insufficient data to allow the correct propagation models to be applied in particular conditions. Use of inappropriate propagation models can lead to many orders of magnitude differences in predictions of the number of animals whose behaviour could be affected by seismic pulses. While such large degrees of uncertainty continue, a precautionary approach to management and regulation should be pursued.