Abstract: 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 bottlenose 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 bottlenose dolphins observed near the bridge.

Key Words: bottlenose dolphin, Tursiops truncatus, behavior, bridge, distribution, explosion, noise

Document Type: Research article

DOI: 10.1578/AM.39.2.2013.174

Page Numbers: 174-186

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