How do sharks use their tails and fins to swim?

Sharks use their bodies and fins in distinct ways to achieve movement, stabilization, and steering.

Propulsion

For fast, powerful swimming, sharks rely on the undulation of their bodies and caudal (tail) fins. This movement is driven by the axial musculature—the epaxial and hypaxial muscle blocks—which makes up a significant portion of the shark's body mass. These muscles are arranged in complex, folded patterns that allow a single contraction to produce curvature across a large part of the body, generating significant thrust.1

Stabilization and Steering

While body undulations provide speed, the appendicular fins are primarily used for slow, precision movements, such as investigating food. These fins also play critical roles in maintaining balance and controlling direction:1
* Stabilization: Fins extending at right angles to the body help control rolling (rotation along the longitudinal axis). The dorsal fin helps prevent yawing (lateral seesawing), provided it is positioned behind the shark's centre of gravity.2
* Steering: The anterolateral fins (such as the pectoral fins) act as the major steering organs, helping to counteract pitching (dorsoventral seesawing) movements.2