The use of Navy range bottom-mounted, bi-directional transducers for long-term, deep-ocean prey mapping

Beaked whales have been shown to be particularly sensitive to mid-frequency active sonar but continue to spend considerable time on Navy training ranges, where exposure to sonar is frequent. Understanding the underlying movements of their prey could help to explain the distribution and abundance patterns seen for beaked whales. Beaked whales are among the deepest diving marine mammals and have been shown to feed near the ocean bottom, at depths up to 3000 m. Typical surface-deployed prey mapping technology is not suitable for probing these deep foraging depths. This pilot study aims to us the bi-directional nodes on Navy hydrophone ranges that were developed for underwater communications as a rudimentary prey mapping system. A 1 ms 2 kHz signal was broadcast on an 8 kHz carrier signal and resulting returns were processed to estimate depths of the reflectors. Data are presented from three different time periods on the Southern California Anti-Submarine Warfare Range.