Annular and spiral bubble nets: A simulation-focused analysis of humpback whale feeding strategies

Abstract

Humpback whales can generate bubbly regions (called bubble nets) via their blowholes, which they appear to exploit via loud vocalizations for feeding purposes. We model this phenomenon as the acoustic excitation of an dilute bubble net of radially varying void fraction. A fully coupled phase-averaging approach is used to compute the bubble response and corresponding acoustics. We first assess the possibility of a sophisticated wave-guidance behavior of high-frequency whale vocalizations within the bubble net. For a small range of flow parameters, the reflections associated with the bubbly region result in an observable wave-guidance behavior, though even then these reflections disperse rapidly. In light of this, we also consider multiple whales surrounding the bubble net, each vocalizing towards its center. We show that for physically realistic configurations, including variations in the bubble net void fraction and number of whales, the bubble net can keep its core region substantially quieter than the exterior. Finally, we investigate the ability of spiral, rather than annular, geometries for keeping the bubble-free region quiet.

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