ИСТИНА

The behavior of cetaceans is observed mainly on the surface, and we know much less about they do underwater. All toothed whales emit sounds for orientation and communication. Localizing these sounds may allow us to track animals underwater. We used a small array of four hydrophones assembled in the shape of a tetrahedron with a 0.6 m distance between them. We measured the phase shift for each pair of hydrophones and used the bearings calculated for six hydrophone pairs to find the horizontal and vertical angles to the direction of the source with 5 degrees precision. Using this method we observed several groups of Baird's beaked whales near Bering Island (Commander Islands, North Pacific) where the continental slope reaches depths of 600-1000 m. The whales were in a multi-group aggregation of 35-45 individuals. During multi-channel audio recordings we made continuous observations, noting direction and distance to the surfaced animals, speed of their traveling, type of activity, dispersion of the group and times of surfacing and diving. The total duration of the recording used for localization was 22 minutes. It allowed us to understand how the whales moved and how their vocal behavior changed when they were underwater, compare to at the surface. We discovered that most of the whales who formed groups on the surface remained together during diving, but distances between them increased. Several whales separated from groups or joined groups during diving. Other whales stayed separate during the entire observation. During diving most of the whales emitted different sounds: clicks with regular intervals (3-10 Hz), clicks with irregular intervals changing sharply from 3 to 10 Hz, fast click trains at 20-100 Hz (buzzes) and whistles. When whales were at the surface, their acoustic activity was considerably reduced; most kept silent, but some emitted irregular clicks or buzzes.