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Open Access Research article

Upside-down swimming behaviour of free-ranging narwhals

Rune Dietz1*, Ari D Shapiro2, Mehdi Bakhtiari3, Jack Orr4, Peter L Tyack2, Pierre Richard4, Ida Grønborg Eskesen1 and Greg Marshall3

Author Affiliations

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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BMC Ecology 2007, 7:14  doi:10.1186/1472-6785-7-14

Published: 19 November 2007

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.