Solitary humpback whales manufacture bubble-nets as tools to increase prey intake

TL;DR

Solitary humpback whales create bubble-nets to catch more prey efficiently without increasing energy use.

Contribution

The study reveals how humpback whales control bubble-net structures to enhance foraging efficiency.

Findings

Bubble-nets consist of internally tangential rings controlled by the whales.

Whales regulate net size and depth to increase prey intake sevenfold.

Increased prey density does not raise energetic expenditure.

Abstract

Several animal species use tools for foraging; however, very few manufacture and/or modify those tools. Humpback whales, which manufacture bubble-net tools while foraging, are among these rare species. Using animal-borne tag and unoccupied aerial system technologies, we examine bubble-nets manufactured by solitary humpback whales (Megaptera novaeangliae) in Southeast Alaska while feeding on krill. We demonstrate that the nets consist of internally tangential rings and suggest that whales actively control the number of rings in a net, net size and depth and the horizontal spacing between neighbouring bubbles. We argue that whales regulate these net structural elements to increase per-lunge prey intake by, on average, sevenfold. We measured breath rate and swimming and lunge kinematics to show that the resulting increase in prey density does not increase energetic expenditure. Our results provide a novel insight into how bubble-net tools manufactured by solitary foraging humpback whales act to increase foraging efficiency.

Figures