Humpback whales eat with their hands

Suspected multiple times by observers and scientists, this feeding technique was finally proven using a drone and a camera attached to the end of a pole. These tools make it possible to observe the movement of fins and prey. The manoeuvres performed by the humpbacks were then analyzed using 3D software.

The images were collected on the east coast of the Gulf of Alaska, in an area where young farm-raised salmon are released. The infrastructure used by this industry – namely the metal platforms that surround the fish pens – allowed researchers to study humpbacks from shore, thereby limiting disturbance.

Between 2016 and 2018, researchers observed pectoral herding in two different humpbacks, which repeated the behaviour on numerous occasions.

In all cases, this technique was preceded by a bubble net, another feeding behaviour: the whales blow bubbles through their blowhole while swimming in circles, creating a circular enclosure that helps trap fish.

This “wall of bubbles” is not impervious, however. Indeed, the first bubbles have time to dissipate before the whale finishes its rotation, creating a gap through which the fish can escape. Additionally, some fish species, even if they are trapped, tend not to cluster in dense schools. This is the case of young salmon – the target of over 90% of pectoral herdings – which remain scattered within the bubble net. Fin usage is therefore thought to maximize the concentration of prey.

The other stages of the technique are very different from one individual to another: “Whale A” engulfs horizontally while “Whale B” engulfs vertically, which also has an impact on fin positioning.

In 2018, other researchers described a feeding technique that also involves the pectoral fins: the trapping technique. Like carnivorous plants, humpback whales tread water passively on the surface, mouth agape, and use their fins to guide their prey. In order to escape predation by seabirds, fish then take refuge in the mouths of humpbacks using this strategy.

But according to the Kosma study, the videos documenting the trapping technique did not clearly show that the fins were being used to push fish toward the mouth rather than as a stabilizer. That’s why this study is believed to be the first to actually prove it.