Diving ecology of sperm whales

在为期3年的研究期间，我们对13头抹香鲸（6头在熊野海岸，7头在小笠原群岛）部署了吸盘式数据记录器。自2000年以来，共获得了18头鲸鱼的数据。小笠原群岛附近抹香鲸的潜水深度具有明显的昼夜规律。他们在白天潜水约800- 1300米，但日落后深度变浅至约400米。数据记录仪获得的垂直水温剖面显示，在北太平洋亚热带模态水和400米左右的深水之间存在一个温跃层，鲸鱼倾向于在夜间潜入温跃层的深度。这片水域的边界被认为集中了进行垂直迁移的生物，包括抹香鲸的猎物。另一方面，在熊野海岸外没有观察到温跃层，我们认为在该地区没有发生生物垂直集中，潜水深度没有显示昼夜变化。在小笠原群岛和熊野岸外，抹香鲸追逐猎物的爆发次数和方向存在显著差异，表明抹香鲸在这两个海域的捕食行为不同。海水淡化率与潜水深度相关。这表明鲸鱼根据潜水深度调整潜水角度。然而，初始下降速率（前120秒的下降速率）120-240秒下降速率与终深相关，而与前几次下潜的终深相关。这表明抹香鲸开始潜水的下降速度，使他们能够达到前一次潜水的底部深度，但根据回声定位信号的信息调整他们的目标深度，鲸鱼在潜水后几分钟开始发出回声定位信号。

We deployed suction-cup attached data loggers to 13 sperm whales (6 off Kumano Coast and 7 off Ogasawara Islands) in this 3-year study period. Data from a total of 18 whales have been obtained since 2000. The sperm whales off Ogasawara Islands showed a clear diel pattern in their diving depths. They dived around 800-1300m in the daytime but the depths shallowed to around 400m just after the sunset. Vertical water temperature profile obtained by the data logger showed a thermocline between North Pacific Subtropical Mode Water and deeper water mass around 400m, and whales tended to dive to the depth of the thermocline at night. This border of water mass is thought to concentrate organisms conducting vertical migration including sperm whales' prey. On the other hand, thermocline was not observed off Kumano Coast and we consider that vertical concentration of organisms does not occur in this area and the dive depths do not show diel changes. There were significant differences in the number and direction of the burst, which indicates chase event for prey, between off Kumano Coast and Ogasawara Islands, suggesting sperm whales take different prey in these two areas. Descend rate was correlated with dive depth. This indicates whales adjust dive angle according to the dive depth. However initial descent rate (descent rate in the first 120 sec.) was not correlated with terminal dive depth, but with final bottom depth of the former dives and descent rate in the 120-240 sec was correlated with terminal depth. This suggests sperm whales start a dive with a descent rate so that they can reach bottom depth of the former dive, but adjust their target depth according to the information from echolocation signals, which whales start to emit a few minutes after the submergence.