Hydrodynamic fin function of brief squid, Lolliguncula brevis

Area of Science:

• Marine Biology
• Biomechanics
• Fluid Dynamics

Background:

• The pulsed jet is recognized as a primary mode of squid locomotion.
• The specific contribution of lateral fins to squid swimming dynamics remains incompletely understood.
• Fin morphology and movement patterns exhibit significant diversity across squid species.

Purpose of the Study:

• To investigate the hydrodynamic functions of lateral fins in the brief squid, Lolliguncula brevis.
• To elucidate the role of fins in generating thrust, lift, and stability during swimming.
• To characterize different fin movement modes and their associated flow dynamics.

Main Methods:

• Utilized a water tunnel to observe Lolliguncula brevis swimming at controlled speeds.
• Employed digital particle image velocimetry (DPIV) to analyze water flow patterns around the fins.
• Quantified fin-generated forces by analyzing wake vorticity fields.

Main Results:

• Identified four distinct fin wake patterns (fin modes I-IV) with unique vortical structures.
• Observed all four fin modes during tail-first swimming and modes II and III during arms-first swimming.
• Demonstrated that fins generate varying horizontal and vertical forces, providing lift and thrust depending on speed and orientation.

Conclusions:

• Squid lateral fins are integral to locomotion, producing forces through distinct hydrodynamic modes.
• During tail-first swimming, fins act as stabilizers at low speeds and propulsors at higher speeds, generating net lift.
• During arms-first swimming, fins primarily contribute to lift, with a lesser role in thrust generation.