Upside-down swimming behaviour of free-ranging narwhals |
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Authors: | Rune Dietz Ari D Shapiro Mehdi Bakhtiari Jack Orr Peter L Tyack Pierre Richard Ida Grønborg Eskesen Greg Marshall |
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Affiliation: | 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
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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: 61100%). 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. |
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