Do some cetacean species hunt cooperatively?

Cooperative hunting is one of the most sophisticated behaviours observable in the animal kingdom, a behaviour that calls for communication, planning, shared roles and mutual trust. Among cetaceans it reaches great refinement in several species. From the killer whale that practises Antarctic wave washing to the humpback whale that builds bubble nets in Alaska, by way of the dolphin that herds its prey towards the shore, the diversity of techniques makes this a fascinating question.

Killer whales: the undisputed champions

No cetacean deploys as many cooperative techniques as the killer whale. Depending on the ecotype and the region, it practises a remarkable range: carousel feeding in Norway, where several killer whales encircle a shoal of herring to concentrate it into a tight ball and trap it; strand feeding on the beaches of Argentina or the Crozet Islands to catch sea lions and elephant seals; Antarctic wave washing to slide a seal off a plate of ice; and, documented more recently, coordinated attacks on great white sharks in South Africa.

What is striking beyond the variety is the coordination. Each killer whale has its role in the attack. One will distract or push, another will strike, another will keep watch. Repeated observations show that these roles are not drawn at random: they are assigned in a relatively stable way, with certain individuals having specialities. This planning reflects an exceptional social intelligence.

Humpback whales: the bubble net

The humpback whales (Megaptera novaeangliae) of south-east Alaska and of the Antarctic practise one of the most spectacular cooperative hunts: bubble net feeding. Several whales dive together beneath a shoal of herring or a swarm of krill. One of them turns in a rising spiral while releasing a wall of air bubbles from its blowhole, creating an invisible “cage” that traps the prey. Another gives a deep, powerful call that concentrates them further towards the centre. All the whales then rise at the same moment, mouths wide open, through the trapped shoal.

A single collective mouthful of this kind can feed several whales for the day. The precision of the synchronisation, the division of roles (blower, caller, chargers) and the energy efficiency make this technique one of the finest examples of animal culture. It is passed on by social learning, from mother to calf and between individuals, and it is not practised by every humpback whale population, which is evidence that it is cultural rather than genetic.

Dolphins: herding and other tactics

Common bottlenose dolphins and other delphinids also practise cooperative hunts. On the east coast of the United States, strand feeding (hunting by deliberate beaching) is documented in South Carolina and in Georgia: groups of dolphins encircle a shoal of fish and drive it vigorously towards the shore, creating a wave that throws the fish onto the muddy bank. The dolphins then rush half aground to seize them, before sliding back into the water.

In the Strait of Gibraltar, the resident killer whales practise a particularly spectacular hunt for bluefin tuna: several individuals pursue an adult tuna for kilometres until it is exhausted. This technique calls for a collective stamina and persistence that the tuna, despite its higher top speed, ends up unable to sustain.

Cooperation even with humans

One of the most extraordinary cases is that of Laguna, in Brazil. Since the 19^th century, a local population of common bottlenose dolphins has cooperated with human fishers to catch mullet. The dolphins drive the fish towards the nets held by the fishers in shallow water, signalling the moment to cast by a characteristic dive. The fishers then feed the dolphins with part of the catch.

This interspecific cooperation, passed on for nearly 200 years between dolphins and between fishing families, is unique in the world. It is now threatened by pollution and urbanisation, and several scientific studies are seeking to preserve this exceptional biological and cultural heritage.

Instinct or learning?

The large question remains the respective part of instinct and of learning. The answer appears clear for most of the documented techniques: they are learned, not innate. Young killer whales watch their elders for years before taking an active part. Young humpback whales do not take up bubble net feeding spontaneously, they imitate it. The strand feeding of the South Carolina dolphins is practised only by certain maternal families, forming local “hunting schools”.

This cultural dimension of cooperative hunting among cetaceans brings their societies closer to ours, where social learning passes knowledge from one generation to the next. Beyond the spectacle, it is one of the fundamental reasons why the conservation of cetaceans matters so much: every population lost takes with it a unique body of know-how, gone for good.

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