Simulation of humpback whale bubble-net feeding models

TL;DR

This paper models humpback whale bubble-net feeding using a coupled flow and acoustics simulation, analyzing waveguiding mechanisms, configurations of multiple whales, and spiral nets to understand acoustic behaviors and optimize feeding strategies.

Contribution

It introduces a comprehensive simulation approach to study bubble-net feeding, assessing waveguiding and acoustic effects for various configurations and parameters.

Findings

Reflections cause waveguiding only in limited conditions.

Multiple whales can keep the net quieter, but require cooperation.

Spiral nets can guide vocalizations effectively without cooperation.

Abstract

Humpback whales can generate intricate bubbly regions, called bubble nets, via their blowholes. They appear to exploit these bubble nets for feeding via loud vocalizations. A fully-coupled phase-averaging approach is used to model the flow, bubble dynamics, and corresponding acoustics. A previously hypothesized waveguiding mechanism is assessed for varying acoustic frequencies and net void fractions. Reflections within the bubbly region result in observable waveguiding for only a small range of flow parameters. A configuration of multiple whales surrounding and vocalizing towards an annular bubble net is also analyzed. For a range of flow parameters the bubble net keeps its core region substantially quieter than the exterior. This approach appears more viable, though it relies upon the cooperation of multiple whales. A spiral bubble net configuration that circumvents this requirement is also investigated. The acoustic wave behaviors in the spiral interior vary qualitatively with the vocalization frequency and net void fraction. The competing effects of vocalization guiding and acoustic attenuation are quantified. Low void fraction cases allow low-frequency waves to partially escape the spiral region, with the remaining vocalizations still exciting the net interior. Higher void fraction nets appear preferable, guiding even low-frequency vocalizations while still maintaining a quiet net interior.