Payne Braedon, Keller Bryan A, Weihs Daniel, Gurka Roi
Deprtament of Physics and Engineering Science Coastal Carolina University Conway South Carolina USA.
NOAA Fisheries Office of International Affairs, Trade, and Commerce Washington DC USA.
Ecol Evol. 2025 Jun 27;15(7):e71660. doi: 10.1002/ece3.71660. eCollection 2025 Jul.
We present a novel method of measuring thrust of aquatic animals using in situ video data of swimming motions. To demonstrate its utility, the method was applied to several large elasmobranch species, which are typically highly challenging to measure. Using motion tracking software, we analyzed video footage of wild and captive sharks to track their instantaneous position and speed. In order to estimate the force output, we used the tail/body motion based on the swimming modes of the fish to calculate the water displaced by this motion during locomotion. Using Newton 3rd law, we have calculated the instantaneous force exerted by the water on the shark. The force output, that is thrust was calculated by averaging the instantaneous force over the tailbeat cycle. The thrust, for each fish was converted into a nondimensional parameter defined as: scaled thrust, allowing comparisons independent of size based on prior knowledge of the fish length and mass. This scaled thrust was analyzed for various swimming modes and caudal fin morphology to correlate to behavioral features through principal component analysis (PCA) we demonstrate the coupling between morphological traits and hydrodynamic forces. For the species studied the ratio of the upper to lower lobe of the caudal fin (CLAR) emerged as a strong predictor of scaled thrust, accounting for more than 80% of the observed variation. Our findings for the species studied indicate that coastal pelagic species exhibited lower scaled thrust values than benthic species, suggesting that benthic species may be less efficient, expending more energy to remain aloft or compensate for drag relative to generating forward motion. We propose that the unique ecological niches of these species drive behavioral changes that result in morphological adaptations to optimize performance.
我们提出了一种利用游泳运动的现场视频数据测量水生动物推力的新方法。为了证明其效用，该方法被应用于几种大型板鳃亚纲物种，这些物种通常极难测量。使用运动跟踪软件，我们分析了野生和圈养鲨鱼的视频片段，以跟踪它们的瞬时位置和速度。为了估计力的输出，我们根据鱼类的游泳模式，利用尾巴/身体的运动来计算运动过程中该运动所排开的水量。利用牛顿第三定律，我们计算了水对鲨鱼施加的瞬时力。通过对尾拍周期内的瞬时力进行平均来计算力的输出，即推力。对于每条鱼，将推力转换为一个无量纲参数，定义为：缩放推力，基于对鱼的长度和质量的先验知识，使得可以独立于大小进行比较。通过主成分分析（PCA）对各种游泳模式和尾鳍形态的缩放推力进行分析，以将其与行为特征相关联，我们证明了形态特征与水动力之间的耦合。对于所研究的物种，尾鳍上叶与下叶的比例（CLAR）成为缩放推力的一个强有力的预测指标，占观察到的变异的80%以上。我们对所研究物种的研究结果表明，沿海中上层物种的缩放推力值低于底栖物种，这表明底栖物种可能效率较低，相对于产生向前运动而言，需要消耗更多能量来保持在水中或补偿阻力。我们认为，这些物种独特的生态位驱动了行为变化，从而导致形态适应以优化性能。
