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Upside-down swimming behaviour of free-ranging narwhals.

Dietz R, Shapiro AD, Bakhtiari M, Orr J, Tyack PL, Richard P, Eskesen IG, Marshall G - BMC Ecol. (2007)

Bottom Line: 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, Postbox 358, DK-4000 Roskilde, Denmark. rdi@dmu.dk

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.

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Narwhal orientation during diving. Diving record for animals outfitted with DTAG with dorsal and ventral sides up indicated by dark blue and red, respectively (see text for details on their calculation). Portions of the dive with roll values that did not fall into these two categories are grey. Note the different ranges on the time axes.
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Figure 3: Narwhal orientation during diving. Diving record for animals outfitted with DTAG with dorsal and ventral sides up indicated by dark blue and red, respectively (see text for details on their calculation). Portions of the dive with roll values that did not fall into these two categories are grey. Note the different ranges on the time axes.

Mentions: The DTAG allowed a more precise quantification of the orientation of the two tagged male narwhals during entire dive sequences (Table 2), but yielded no information about when the animal was swimming along the inlet bottom. A quantitative assessment of the proportion of time spent swimming dorsal versus ventral side up yielded average percentages of 58% vs. 13% (#37232: 53% vs. 18%; #37233: 65% vs. 9%) from the DTAG sample. The remaining 29% of the time the animals had intermediate orientations while moving between the normal or upside-down orientation. The tagged whale was oriented upside-down 70% of the time during the descent period of the dives (#37232: 87%; #37233: 56%) and an average of 77% of the time during the initial 60% of the time of the dive (defined as a vertical excursion exceeding 20 m; #37232: 89%, #37233: 65%). Figure 3 illustrates when the two animals with a DTAG were oriented dorsal or ventral side up for the entire diving sequence. Figure 4 focuses on a single dive of each animal to illustrate their complex roll dynamics. Individual #37232 rotated to a supine orientation and remained upside-down for the majority of the dive between roughly 45 and 105 m before ascending and rolling slightly to spend the last portion of its ascent dorsal side up. Individual #37233 corkscrewed continuously on the descent, rolling repeatedly before reaching a maximum depth of ~113 m. Between recorded times of 36.5 and 37.5 min, his supine orientation coincided with a relatively level depth, suggesting he may have been moving along a flat seabed at that time. His return to the surface was unremarkable in terms of roll as he remained dorsal side up during nearly the entire ascent.


Upside-down swimming behaviour of free-ranging narwhals.

Dietz R, Shapiro AD, Bakhtiari M, Orr J, Tyack PL, Richard P, Eskesen IG, Marshall G - BMC Ecol. (2007)

Narwhal orientation during diving. Diving record for animals outfitted with DTAG with dorsal and ventral sides up indicated by dark blue and red, respectively (see text for details on their calculation). Portions of the dive with roll values that did not fall into these two categories are grey. Note the different ranges on the time axes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2238733&req=5

Figure 3: Narwhal orientation during diving. Diving record for animals outfitted with DTAG with dorsal and ventral sides up indicated by dark blue and red, respectively (see text for details on their calculation). Portions of the dive with roll values that did not fall into these two categories are grey. Note the different ranges on the time axes.
Mentions: The DTAG allowed a more precise quantification of the orientation of the two tagged male narwhals during entire dive sequences (Table 2), but yielded no information about when the animal was swimming along the inlet bottom. A quantitative assessment of the proportion of time spent swimming dorsal versus ventral side up yielded average percentages of 58% vs. 13% (#37232: 53% vs. 18%; #37233: 65% vs. 9%) from the DTAG sample. The remaining 29% of the time the animals had intermediate orientations while moving between the normal or upside-down orientation. The tagged whale was oriented upside-down 70% of the time during the descent period of the dives (#37232: 87%; #37233: 56%) and an average of 77% of the time during the initial 60% of the time of the dive (defined as a vertical excursion exceeding 20 m; #37232: 89%, #37233: 65%). Figure 3 illustrates when the two animals with a DTAG were oriented dorsal or ventral side up for the entire diving sequence. Figure 4 focuses on a single dive of each animal to illustrate their complex roll dynamics. Individual #37232 rotated to a supine orientation and remained upside-down for the majority of the dive between roughly 45 and 105 m before ascending and rolling slightly to spend the last portion of its ascent dorsal side up. Individual #37233 corkscrewed continuously on the descent, rolling repeatedly before reaching a maximum depth of ~113 m. Between recorded times of 36.5 and 37.5 min, his supine orientation coincided with a relatively level depth, suggesting he may have been moving along a flat seabed at that time. His return to the surface was unremarkable in terms of roll as he remained dorsal side up during nearly the entire ascent.

Bottom Line: 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, Postbox 358, DK-4000 Roskilde, Denmark. rdi@dmu.dk

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.

Show MeSH
Related in: MedlinePlus