The Relationship of Land Based Explosions Mimicking 155 mm Artillery on Offshore Beluga Whale Hearing Threshold
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The Eagle River Flats is an impact region for artillery at Fort Richardson, Alaska. Adjacent to the Flats is the Knik Arm of Cook Inlet, which is the habitat for a distinct population of beluga whales, Delphinapterus leucas. Research has established noise thresholds at which the beluga whales’ hearing may become impaired or injured. In addition, the National Oceanic and Atmospheric Administration’s, National Marine Fisheries Service has set guidelines regarding noise levels that are considered to have serious impacts on marine mammals. In order to assess the effects of 155 mm artillery explosions on the habitat of these whales, a series of 6.8 kg C4 plastique charges were detonated on land 500 meters from the water’s edge. Hydrophones were deployed in the Knik Arm at high and low tied. The received signal 30 meters from the shore in water depths of 8 meters was more intense at high tide, with broadband peak levels of approximately 180 dB re 1 μPa. The dominant frequency was 20 Hz. Using the recorded peak pressure, the intensity at various distances across the Knik Arm of the Cook Inlet was calculated.