%0 Journal Article
%T Upside-down swimming behaviour of free-ranging narwhals
%A Rune Dietz
%A Ari D Shapiro
%A Mehdi Bakhtiari
%A Jack Orr
%A Peter L Tyack
%A Pierre Richard
%A Ida Eskesen
%A Greg Marshall
%J BMC Ecology
%D 2007
%I BioMed Central
%R 10.1186/1472-6785-7-14
%X 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¨C18%) 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.The narwhal (Monodon monoceros) is an Arctic odontocete that can grow up to 5 m long. Males possess a tusk that erupts from the upper left jaw [1]. Individuals with two tusks and females with one or two tusks have also been reported but are rare [1]. The narwhal lacks a dorsal fin, but it has a low, irregular ridge 4¨C5 cm high along the posterior half of the back [1]. Narwhals inhabit the inshore bays and island passages of northeastern Canada, Greenland and Svalbard from July through September [2-5]. In the autumn, as Arctic fjords and bays begin to freeze, narwhals vacate these areas and migrate long distances to their wintering areas, which are further south and in deeper water [6-9]. During the winter and spring (November-June), narwhals frequent areas covered with dense (up to 99%) offshore pack ice e.g., [10,11]. Over the last 13 years, satellite tracking studies have provided information about narwhal seasonal and stock distribution as well as migration routes and dive behaviour [6-9,11-14].Data from satellite-linked time depth recorders (STDRs) and diving archival tags have been used to describe narwhal diving behaviour and derive correction factors for submerged animals when formulating population est
%U http://www.biomedcentral.com/1472-6785/7/14