School of Biological Sciences, The University of Queensland, St Lucia, QLD 4072, Australia
Biol Open. 2014 Sep 4;3(10):887-94. doi: 10.1242/bio.20149480.
Hatchling sea turtles emerge from nests, crawl down the beach and enter the sea where they typically enter a stereotypical hyperactive swimming frenzy. During this swim the front flippers are moved up and down in a flapping motion and are the primary source of thrust production. I used high-speed video linked with simultaneous measurement of thrust production in tethered hatchlings, along with high-speed video of free swimming hatchlings swimming at different water speeds in a swim flume to investigate the links between kinematics of front flipper movement, thrust production and swimming speed. In particular I tested the hypotheses that (1) increased swimming speed is achieved through an increased stroke rate; (2) force produced per stroke is proportional to stroke amplitude, (3) that forward thrust is produced during both the down and up phases of stroking; and (4) that peak thrust is produced towards the end of the downstroke cycle. Front flipper stroke rate was independent of water speed refuting the hypothesis that swimming speed is increased by increasing stroke rate. Instead differences in swimming speed were caused by a combination of varying flipper amplitude and the proportion of time spent powerstroking. Peak thrust produced per stroke varied within and between bouts of powerstroking, and these peaks in thrust were correlated with both flipper amplitude and flipper angular momentum during the downstroke supporting the hypothesis that stroke force is a function of stroke amplitude. Two distinct thrust production patterns were identified, monophasic in which a single peak in thrust was recorded during the later stages of the downstroke, and biphasic in which a small peak in thrust was recorded at the very end of the upstroke and this followed by a large peak in thrust during the later stages of the downstroke. The biphasic cycle occurs in ∼20% of hatchlings when they first started swimming, but disappeared after one to two hours of swimming. The hypothesis that forward thrust is produced during both the up and down stroke was only supported relatively rarely in hatchlings that exhibited the diphasic cycle, the majority of time forward thrust was only produced during the downstroke phase. The hypothesis that peak forward thrust is produced during the end of the downstroke was supported in both the monophasic and biphasic thrust producing stroke cycles.
幼龟从巢穴中孵化出来，爬下海滩，进入大海，在那里它们通常会进入一种典型的极度活跃的游泳狂潮。在这段游泳过程中，前鳍会上下扇动，这是产生推力的主要来源。我使用高速视频，结合对系留幼龟的推力产生的同步测量，以及在游泳水槽中以不同水速游泳的自由游动幼龟的高速视频，研究了前鳍运动的运动学、推力产生和游泳速度之间的联系。特别是，我测试了以下假设：（1）通过增加划水频率来提高游泳速度；（2）每次划水产生的力与划水幅度成正比；（3）在划水的上下两个阶段都产生向前的推力；（4）最大推力产生在划水周期的下降阶段的末端。前鳍划水频率与水速无关，这否定了游泳速度通过增加划水频率来提高的假设。相反，游泳速度的差异是由鳍幅的变化和动力划水时间比例的组合引起的。每次划水产生的峰值推力在动力划水的单次和多次之间有所不同，这些峰值推力与下降阶段的鳍幅和鳍角动量相关，支持了划力是划水幅度的函数的假设。确定了两种不同的推力产生模式，单相模式在下降阶段的后期记录到一个单一的峰值推力，双相模式在上升阶段的末期记录到一个小的峰值推力，随后在下降阶段的后期记录到一个大的峰值推力。当幼龟刚开始游泳时，大约 20%的幼龟会出现双相周期，但在游泳一到两个小时后，这种现象就消失了。只有在表现出双相周期的幼龟中，前推力在上下两个阶段都产生的假设才得到了相对较少的支持，大多数情况下，前推力只在下降阶段产生。在单相和双相产生推力的划水周期中，最大前推力产生于下降阶段末端的假设得到了支持。
