Abstract:

The harbor porpoise (Phocoena phocoena) is a small toothed whale living mostly in coastal waters. There are large, but unknown, numbers in the inner Danish waters. Four are in captivity at Fjord Belt Center, Kerteminde, Denmark, one of which was born there in 2006. Harbor porpoises use their ultrasonic clicks as biosonar for orientation and detection of prey (mostly smaller pelagic and bottom dwelling fish), and for communication. For studying wild animals, hydrophone arrays [Villadsgaard , J. Exp. Biol. 210 (2007)] and acoustic (time∕depth) tags [Akamatsu , Deep Sea Res. 2 (2007)] have been used. For studying captive animals, arrays and video techniques [Verfuss , J. Exp. Biol. 208 (2005)], as well as miniature acoustic-behavioral tags [Deruiter , J. Acoust. Soc. Am 123 (2008)], have been used. While searching for prey, harbor porpoises use clicks at long intervals (50 ms) that progressively decrease when closing an object. After detecting the prey, the click interval stabilizes and then becomes progressively shorter while approaching the prey. The sequence ends in a terminal high-repetition rate buzz (500 clicks/s) just before capturing the prey (a video will be shown). The temporal sequence differs from that of beaked whales but is similar to that of bats.