Acoustic predation in a sailfish-flying fish cloak

Area of Science:

• Fluid dynamics
• Bioacoustics
• Animal behavior

Background:

• Sailfish corral flying fish using a vortex near the ocean surface.
• This action creates a unique pattern of arced surface waves.
• The reason behind this phenomenon has remained unexplained.

Purpose of the Study:

• To investigate the mechanism behind the acoustic cloaking effect used by sailfish.
• To understand how sailfish disorient flying fish using fluid dynamics and acoustics.
• To explain the formation of surface waves during sailfish predation.

Main Methods:

• Acoustic modeling of vortex dynamics and pressure release.
• Analysis of fluid mechanics involved in fish motion and vortex interaction.
• Comparison with vibrations induced in a cup of water.

Main Results:

• Sudden cessation of fish motion leads to vortex interaction and pressure release, forming an acoustic monopole.
• The sailfish and flying fish bodies act as acoustic mirrors, creating a disorienting sound field.
• This acoustic cloak prevents flying fish from sensing wind direction, hindering their escape.

Conclusions:

• The observed surface waves are a manifestation of acoustic radiation from the monopole.
• Sailfish employ a sophisticated acoustic strategy to disorient prey.
• Flying fish lack the necessary tail rigidity for a rapid escape from this acoustic manipulation.