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Studies of depredating sperm whales (Physeter macrocephalus) off Sitka, AK, using videocameras, tags, and long-range passive acoustic tracking

  • Author(s): Mathias, Delphine
  • Mathias, Delphine
  • et al.
Abstract

This dissertation uses videocameras, tags and acoustic recorders to investigate the diving and acoustic behavior of sperm whales in the Gulf of Alaska during natural and depredation foraging conditions. First, underwater videocamera footage of a sperm whale attacking a fisherman's longline at 100 m depth was used to examine its acoustic behavior at close range and to estimate its size both acoustically and visually. Second, bioacoustic tagging data demonstrated that the same individuals displayed different acoustic behaviors during natural and depredation foraging states. Two broad categories of depredation, "shallow" and "deep," were also identified. These results suggest that passive acoustic monitoring at close ranges may yield useful metrics for quantifying depredation activity. Third, the behavioral reactions of depredating sperm whales to a variety of acoustic play¬backs generated at relatively low source levels were investigated using bioacoustic tags. Finally, bioacoustic and satellite tag data were used to develop passive acoustic techniques for tracking sperm whales with a short -aperture two-element vertical array. When numeric sound propagation models were exploited, localization ranges up to 35 km were obtained. The tracking methods were also used to estimate the source levels of sperm whale "clicks" and "creaks", predict the maximum detection range of the signals as a function of sea state, and measure the drift of several whales away from a visual decoy

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