Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA, USA.
Department of Environmental Affairs, Branch Oceans and Coasts, Cape Town, South Africa.
Curr Biol. 2017 Jul 10;27(13):R636-R637. doi: 10.1016/j.cub.2017.05.063.
A central paradigm of aquatic locomotion is that cetaceans use fluke strokes to power their swimming while relying on lift and torque generated by the flippers to perform maneuvers such as rolls, pitch changes and turns [1]. Compared to other cetaceans, humpback whales (Megaptera novaeangliae) have disproportionately large flippers with added structural features to aid in hydrodynamic performance [2,3]. Humpbacks use acrobatic lunging maneuvers to attack dense aggregations of krill or small fish, and their large flippers are thought to increase their maneuverability and thus their ability to capture prey. Immediately before opening their mouths, humpbacks will often rapidly move their flippers, and it has been hypothesized that this movement is used to corral prey [4,5] or to generate an upward pitching moment to counteract the torque caused by rapid water engulfment [6]. Here, we demonstrate an additional function for the rapid flipper movement during lunge feeding: the flippers are flapped using a complex, hydrodynamically active stroke to generate lift and increase propulsive thrust. We estimate that humpback flipper-strokes are capable of producing large forward oriented forces, which may be used to enhance lunge feeding performance. This behavior is the first observation of a lift-generating flipper-stroke for propulsion cetaceans and provides an additional function for the uniquely shaped humpback whale flipper.
水生动物运动的一个中心范式是，鲸类动物使用尾鳍 strokes 来为游泳提供动力，而依靠鳍状肢产生的升力和扭矩来进行翻滚、俯仰变化和转弯等机动动作[1]。与其他鲸类动物相比，座头鲸（Megaptera novaeangliae）的鳍状肢比例特别大，具有额外的结构特征，以帮助提高水动力性能[2,3]。座头鲸使用杂技般的冲刺动作来攻击密集的磷虾或小鱼群，它们的大鳍状肢被认为提高了它们的机动性，从而提高了捕食猎物的能力。在张开嘴之前，座头鲸通常会快速移动它们的鳍状肢，有人假设这种运动是用来驱赶猎物[4,5]或产生向上的俯仰力矩，以抵消快速吞水产生的扭矩[6]。在这里，我们展示了在冲刺进食过程中快速鳍状肢运动的另一个功能：鳍状肢使用复杂的、水动力活跃的 stroke 来产生升力并增加推进推力。我们估计，座头鲸的鳍状肢 strokes 能够产生很大的向前定向力，这可能用于增强冲刺进食的性能。这种行为是为推进型鲸目动物观察到的第一个产生升力的鳍状肢 stroke，为独特形状的座头鲸鳍状肢提供了额外的功能。
