Trapped within a 'wall of sound': a possible mechanism for the bubble nets of the humpback whales
Leighton, Timothy G., Richards, Simon D. and White, Paul R. (2004) Trapped within a 'wall of sound': a possible mechanism for the bubble nets of the humpback whales. Acoustics Bulletin, 29, (1), 24-29.
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It has been known for decades that, to trap prey, humpback whales sometimes employ ‘bubble nets’ in the form of hollow cylinders. The cylinder wall contains a dense population of bubbles, but the interior is comparatively bubble-free. A group of
whales may cooperate, diving and then rising in a helix, releasing bubbles to form nets of 3 to 30 metres diameter. The prey congregate in the bubblefree centre and are then consumed by the whales, which rise from below. The imprecision of the explanations of why prey refuse to escape through the walls is probably the reason why, although the
phenomenon is described frequently on the internet, it seldom appears in formal scientific literature. This article suggests that the acoustic properties of the nets warrant investigation, and speculates on possible mechanisms by which the nets might act. For example, the trumpeting calls emitted by the whales, when they produce these nets, may become trapped within the bubble wall, generating high intensities there. These calls (which human reporters have subjectively described as disconcerting and even alarming) are so loud that they resound throughout the hull of any nearby ship. This article shows that, under certain insonification conditions, sound can be concentrated within the wall of the net, leaving the inside of the cylinder (where the fish congregate) almost silent. The natural schooling response of fish to the ‘wall of sound’ which they encounter if they try to leave the trap makes them a compact meal when the whales rise up from beneath, with their mouths open. The possibilities of this, and related acoustical effects, are discussed.
|Subjects:||Q Science > QH Natural history > QH301 Biology
Q Science > QC Physics
|Divisions:||University Structure - Pre August 2011 > Institute of Sound and Vibration Research > Fluid Dynamics and Acoustics
University Structure - Pre August 2011 > Institute of Sound and Vibration Research > Signal Processing and Control
|Date Deposited:||11 Feb 2005|
|Last Modified:||02 Mar 2012 13:03|
|Contributors:||Leighton, Timothy G. (Author)
Richards, Simon D. (Author)
White, Paul R. (Author)
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
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