General, Research, Technology

How do huge whales manage to sneak up on large schools of fish?

In 2019, researchers from HawaiianUniversity of Manoa were able to film the amazing hunting of humpback whales for a large school of small fish. As it turned out, in order to feed each other, whales set up a bubble trap for fish and allow relatives to pass through a school of fish with their mouths wide open. But scientists still did not know how so huge marine mammals manage to imperceptibly approach agile fish and not scare them away. The search for an answer to this question was undertaken by American scientists, led by whale expert Jeremy Goldbogen. The answer was found after a small experiment.

The body weight of humpback whales reaches 30,000 kilograms

Its essence and results were described inthe scientific journal PNAS. It is known that humpback whales feed mainly on anchovies, the length of which practically does not exceed 20 centimeters. Despite their small size, for huge 16-meter humpback whales, they are still a welcome prey, because they like to gather in jambs for several hundred individuals. Having passed through such a group of fish with an open mouth, whales can enjoy 30-60% of the whole school, which is enough for them to be full.

Why are the whales so inconspicuous?

As mentioned above, scientists have long beenI wonder how the whales manage to quietly swim to a sensitive flock of tiny and agile fish. The fact is that anchovies have been fleeing predators for millions of years and during this time they learned to avoid sea lions and other animals. However, for all this time they have not developed a strategy for the rapid detection and avoidance of whales.

By the way, earlier the team of Jeremy Goldbogen managed to fix the camera on the back of the whale

According to researchers, the secret of hugemammals lurks in the size of their torso. They suggested that anchovies simply do not have time to notice and be frightened by the approaching whales, because their huge bodies even from afar seem to be motionless spots, which increase too slowly. But the relatively small bodies of sea lions and other predators can be noticed much earlier, because when swimming they perform much more maneuvers than whales.

Sea lions are clearly smaller than whales in size

This assumption was verified duringlaboratory experiment. Researchers placed small fish in an aquarium and showed them images of approaching predators in the form of spots of different sizes. As it turned out, fish really respond faster to small moving spots, while large objects are most often simply ignored by them. This is their mistake - they are simply unable to notice the slowly approaching carcasses of huge whales. And when the predators open their mouths, it becomes too late, and many of the anchovies become victims.

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After the experiment, the researchersdecided to follow the behavior of anchovies in nature. It turned out that when huge predators approach a school of fish, the small inhabitants of the seas are really unaware of the impending danger. However, once they see a smaller predator swimming towards them, they swim in a scattering manner.