Upside-down swimming behaviour of free-ranging narwhals.
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.


CONCLUSIONS
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.
Dietz
Rune
R
Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, Postbox 358, DK-4000 Roskilde, Denmark. rdi@dmu.dk
Shapiro
Ari D
AD
Bakhtiari
Mehdi
M
Orr
Jack
J
Tyack
Peter L
PL
Richard
Pierre
P
Eskesen
Ida Grønborg
IG
Marshall
Greg
G
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D005260:Female; D008297:Male; D009949:Orientation; D011187:Posture; D013550:Swimming / Q000502:physiology*; D014907:Whales / Q000502:physiology*