University of Rostock, Institute for Biosciences, 18059 Rostock, Germany.
J Exp Biol. 2010 Nov 1;213(Pt 21):3734-40. doi: 10.1242/jeb.047134.
The mystacial vibrissae of harbour seals (Phoca vitulina) constitute a highly sensitive hydrodynamic receptor system enabling the seals to detect and follow hydrodynamic trails. In the wild, hydrodynamic trails, as generated by swimming fish, consist of cyclic burst-and-glide phases, associated with various differences in the physical parameters of the trail. Here, we investigated the impact of glide phases on the trackability of differently aged hydrodynamic trails in a harbour seal. As fish are not easily trained to swim certain paths with predetermined burst-and-glide phases, the respective hydrodynamic trails were generated using a remote-controlled miniature submarine. Gliding phases in hydrodynamic trails had a negative impact on the trackability when trails were 15 s old. The seal lost the generated trails more often within the transition zones, when the submarine switched from a burst to a glide moving pattern. Hydrodynamic parameter analysis (particle image velocimetry) revealed that the smaller dimensions and faster decay of hydrodynamic trails generated by the gliding submarine are responsible for the impaired success of the seal tracking the gliding phase. Furthermore, the change of gross water flow generated by the submarine from a rearwards-directed stream in the burst phase to a water flow passively dragged behind the submarine during gliding might influence the ability of the seal to follow the trail as this might cause a weaker deflection of the vibrissae. The possible ecological implications of intermittent swimming behaviour in fish for piscivorous predators are discussed.
港海豹（Phoca vitulina）的触须是一种高度敏感的水动力受体系统，使海豹能够检测和追踪水动力轨迹。在野外，由游泳鱼类产生的水动力轨迹由周期性的爆发-滑行阶段组成，与轨迹的各种物理参数差异有关。在这里，我们研究了滑行阶段对港海豹不同年龄水动力轨迹可追踪性的影响。由于鱼类不容易被训练成按照特定的爆发-滑行阶段游特定的路径，因此使用遥控微型潜艇产生相应的水动力轨迹。当轨迹为 15 秒时，滑行阶段对可追踪性有负面影响。当潜艇从爆发模式切换到滑行移动模式时，海豹在过渡区更频繁地失去生成的轨迹。水动力参数分析（粒子图像测速法）表明，滑行潜艇产生的水动力轨迹尺寸更小，衰减更快，这导致海豹跟踪滑行阶段的成功率降低。此外，潜艇在爆发阶段产生的向后指向水流与滑行阶段被动拖曳在潜艇后面的水流之间的总水流变化，可能会影响海豹跟随轨迹的能力，因为这可能导致触须的偏转减弱。文中还讨论了鱼类间歇性游泳行为对以鱼为食的捕食者的可能生态影响。
