Heterocercal tail function in leopard sharks: a three-dimensional kinematic analysis of two models

Area of Science:

• Ichthyology
• Biomechanics
• Fluid Dynamics

Background:

• Two models exist for heterocercal tail function in sharks: the classical model (dorsal/anterior force) and Thomson's model (ventral/anterior force through center of gravity).
• Understanding tail function is crucial for comprehending shark locomotion and hydrodynamics.

Purpose of the Study:

• To evaluate the classical and Thomson models of heterocercal tail function.
• To describe the three-dimensional kinematics of the leopard shark (Triakis semifasciata) tail during swimming.

Main Methods:

• Utilized two high-speed cameras to capture lateral and posterior views of leopard sharks swimming.
• Tracked eight 3D landmarks on the tail over time to calculate surface orientation and kinematics.
• Employed dye-stream visualization to observe water deflection patterns.

Main Results:

• Anterior tail points showed smaller excursions and earlier peak lateral movement than trailing edge points.
• Terminal tail lobe movement preceded the ventral lobe, aligning with the classical model's predictions.
• Dye visualization confirmed water deflection ventrally and posteriorly, supporting the classical model.

Conclusions:

• The classical model of heterocercal tail function in sharks is strongly supported by this study.
• Three-dimensional kinematic analysis is essential for accurately understanding heterocercal tail function.
• The observed tail movements generate thrust and potentially lift, contributing to efficient shark swimming.