Rorquals at lunch

Three rorquals of the St. Lawrence, three different strategies: although the blue whale, minke whale and fin whale are perhaps all baleen “gulpers”, closer examination reveals that they go about capturing their favourite prey in different ways.

The blue whale feeds almost exclusively on krill. It ingests about 1 tonne a day, up to 4 tonnes. Krill live in deep water during the day and rise to the surface at dusk to spend the night. Currents can sometimes force them to surface in the middle of the day. Blue whales can thus be observed surface feeding: seeing this giant turn onto its side on the water’s surface, its immense mouth agape, is simply breathtaking. This technique requires considerable physical effort: with its gigantic mouth, the blue whale takes in a volume of water equal to its own weight of 90 tonnes. But the gain is estimated to be 90 times greater than the energy spent.

You can see a blue whale feeding on clouds of krill in that video of GEMM Lab, Oregon State University.

The minke whale is also a fascinating species to observe when feeding. It often frequents tide rips, taking advantage of the fish trapped between the cold and warm water masses. It pursues its prey and traps them at the surface. It raises its body half out of the water or emerges on its side, offering observers views of its belly, pectoral fins, half a tail… It adapts its strategies to the environmental conditions (currents, water depth, type of prey), even going so as far as to adopt and specialize in a particular sector.

Fin whales often feed in synchronized groups. In pods consisting of 10 to 20 or more individuals, these large, sleek and speedy rorquals surface in tight formations. They can be observed to form a semi-circle, a bit like a merry-go-round where they briefly dive in succession and then resurface for a new breath of air. The ride ends after a few minutes when, one after another, they arch their backs before diving down into the deep. Does this technique allow fin whales to cooperate to catch fish more efficiently? Or are these animals competing with one another?

Watch a surface feeding video filmed by the Group for Research and Education on Marine Mammals (GREMM), and another filmed by drone, this time off the Costa del Garraf, by the Asociación EDMAKTUB.

Herding

Dolphins and porpoises swim encircle a school of fish to frighten them and force them to regroup. Bubble nets blown by humpback whales also serve to concentrate the fish, which are reluctant to cross this barrier. Lobtailing by dolphins or head-slapping by minke whales on the water surface can also be employed to scare fish. Occasionally, the predators themselves band together to increase their hunting success: killer whales, somewhat like a pack of wolves, will sometimes attack rorquals, sperm whales or gray whales.

Hunting with their eyes closed

Some toothed whales such as the sperm whale are believed to use low-frequency sounds to “stun” their prey before capturing them. This explains why blind sperm whales are not any leaner than other members of their species. The Guiana dolphin, in addition to using echolocation to locate its prey in the turbid waters of the estuaries that it inhabits, is thought to also use passive electroreception: receptors on its rostrum allow it to detect the electric fields of its prey.

Shark Bay and its many techniques

Some individuals learn techniques and then teach it to other members of their community. Bottlenose dolphins in Shark Bay (W. Australia) split up into family clans, some of which have developed their own exclusive hunting techniques. They can be observed practising a behaviour known as “conching”, which consists of inserting their rostrum into the shell of this gastropod and shaking it about for food or to find small fish hidden inside. Others shield their rostrum with a sponge while foraging on the seabeds for sandperches. Others practise “voluntary stranding”, pushing their prey up onto the beach, from which point it cannot escape.

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