Upside-down swimming behaviour of free-ranging narwhals

• Main Authors: Dietz, Rune, Shapiro, Ari D, Bakhtiari, Mehdi, Orr, Jack, Tyack, Peter L, Richard, Pierre, Eskesen, Ida, Marshall, Greg
• Format: Article in Journal/Newspaper
• Language: English
• Published: BioMed Central Ltd. 2007
• Subjects: Admiralty Inlet; Canada; The Tusk; Monodon monoceros; narwhal*
• Online Access: http://www.biomedcentral.com/1472-6785/7/14

Abstract Background Free-ranging narwhals ( Monodon monoceros ) were instrumented in Admiralty Inlet, Canada with both satellite tags to study migration and stock separation and short-term, high-resolution digital archival tags to explore diving and feeding behaviour. Three narwhals were equipped with an underwater camera pod (Crittercam), another individual was equipped with a digital archival tag (DTAG), and a fifth with both units during August 2003 and 2004. Results Crittercam footage indicated that of the combined 286 minutes of recordings, 12% of the time was spent along the bottom. When the bottom was visible in the camera footage, the narwhals were oriented upside-down 80% of the time (range: 61 100%). The DTAG data (14.6 hours of recordings) revealed that during time spent below the surface, the two tagged narwhals were supine an average of 13% (range: 9–18%) of the time. Roughly 70% of this time spent in a supine posture occurred during the descent. Conclusion Possible reasons for this upside-down swimming behaviour are discussed. No preference for a clockwise or counter-clockwise direction of roll was observed, discounting the possibility that rolling movements contribute to the asymmetric left-handed helical turns of the tusk.