Upside-down swimming behaviour of free-ranging narwhals
1 Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, Postbox 358, DK-4000 Roskilde, Denmark
2 Biology Department, Woods Hole Oceanographic Institution, MS #50, Woods Hole, MA 02543, USA
3 National Geographic Remote Imaging, 1145 17th St. NW, Washington, DC 20036, USA
4 Department of Fisheries and Oceans, Central and Arctic Region, Arctic Research Division, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada
BMC Ecology 2007, 7:14 doi:10.1186/1472-6785-7-14Published: 19 November 2007
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.
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.
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.