Abstract

(…) Several researchers have obtained accurate speed data on unconfined cetaceans using a variety of techniques. Hui (1989) analyzed video tapes of Delphinus delphis and Stenella attenuata filmed from a ship. Au et al. (1988) analyzed the splash remnants on an aerial photograph taken of porpoising S. attenuata. In this study we present behaviors and swimming speeds of wild Dall’s porpoises (Phocoenoides dalli) measured from an inflatable boat.

Little is known about the swimming behavior of Dall’s porpoises, in part because of their offshore distribution (Jefferson 1987). Since they are difficult
to see at a distance, P. dalli are most commonly observed while playing in the bow waves of boats (Leatherwood et al. 1982). However, some researchers have obtained general descriptions of behavior for P. dalli (Morejohn 1979; Bouchet et al. 1984; Jefferson 1987, 1988; Miller 1988). Three characteristic surfacing behaviors have been documented for Dall’s porpoises: slow rolling, fast rolling, and rooster-tailing. The speeds at which all three behaviors occur have not previously been reported. (…)