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.

中文翻译：

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自由放养的独角鲸的倒置游泳行为。

背景 自由放养的独角鲸（Monodon monoceros）在加拿大海军部入口安装了卫星标签以研究迁徙和种群分离，并使用短期、高分辨率数字档案标签来探索潜水和进食行为。三只独角鲸配备了水下摄像机吊舱 (Crittercam)，另一只独角鲸配备了数字档案标签 (DTAG)，第五只独角鲸在 2003 年 8 月和 2004 年期间同时配备了两个装置。结果 Crittercam 镜头显示总共 286 分钟的记录, 12% 的时间花在底部。当底部在相机镜头中可见时，独角鲸有 80% 的时间是倒置的（范围：61 100%）。DTAG 数据（14.6 小时的记录）显示，在地表以下的时间里，两只带标签的独角鲸平均有 13%（范围：9-18%）的时间仰卧。大约 70% 的仰卧姿势发生在下降过程中。结论 讨论了这种倒置游泳行为的可能原因。没有观察到对顺时针或逆时针方向滚动的偏好，排除了滚动运动导致象牙不对称左旋螺旋转动的可能性。