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Marine seismic surveys, which use loud, primarily low-frequency sound to penetrate the sea floor, are known to disturb and could harm marine life. The use of these surveys for conventional and alternative offshore energy development as well as research is expanding. Given their proliferation and potential for negative environmental impact, there is a growing need for systematic planning and operational standards to eliminate or at least minimize impacts, especially when surveys occur in sensitive areas. Mitigating immediate impacts is obviously critical, but monitoring for short- as well as long-term effects and impacts is also needed. Regulatory requirements for both mitigation and monitoring vary widely from one country or jurisdiction to another. Historically, most have focused on acute effects but share a common objective of minimizing potential adverse impacts. Specific examples in different areas are given to illustrate general approaches for predicting, minimizing, and measuring impacts for operations in essentially any marine environment. The critical elements of a robust mitigation and monitoring plan for responsibly conducting marine seismic surveys include obtaining baseline ecological data; substantial advance planning, communication, and critical review; integrated acoustic and visual monitoring during operations; and systematic analysis of results to inform future planning and mitigation. [ABSTRACT FROM AUTHOR]

Construction and demolition activities are commonplace in offshore and coastal waters, in habitats that are important feeding and breeding grounds for marine mammals. In Sarasota Bay, Florida, the construction of a large fixed-span bridge was completed in July 2003, followed by two in-air explosions and a final underwater explosion to demolish the pre-existing drawbridge. Boat-based surveys were conducted to compare distribution of bottle-nose dolphin (Tursiops truncatus) sightings during bridge construction and demolition to historical sighting records. Additionally, underwater sound pressure levels were monitored at six listening stations to the north and south of the bridge. Dolphin density in the vicinity of the bridge was significantly higher after construction was completed than during construction. The few bottlenose dolphins that used the waters in the general vicinity of the bridge during construction did not appear to avoid the bridge, suggesting that some bottlenose dolphins may still have preferred the habitat around the bridge despite the construction and demolition noise. During the underwater detonation, the small sample of observed bottlenose dolphins decreased nearest neighbor distance, increased group size, and exhibited heading changes. The underwater explosion, which was contained by a steel coffer-cell, was quieter under water than were both in-air explosions, also measured under water. Based on these results, in-air explosions occurring close to water level (< 5 m) should be considered for their potential to effect marine mammals. These explosions and persistent noise associated with construction and/or demolition operations could have contributed to the change in density of the bottle-nose dolphins observed near the bridge. [ABSTRACT FROM AUTHOR]