Fish in a large flock are very sensitive, which allows them to instantly escape from an approaching predator. Why is this so, recently discovered by American scientists.
Fish gather in numerous schools. This is one of the forms of protection: it allows them to respond to the approach of a predator and to defend themselves in a timely manner. But such a strategy is ineffective against 15-meter whales. He suddenly comes close to a school of small fish and is able to swallow most of the colony.
It seems incredible at first glance. After all, small anchovy fish have developed this form of protection for tens of millions of years. Features of the hunting strategy of whales and the behavior of anchovies were studied by the biologist J. Goldbogen and his colleagues working at Stanford University, located in California, USA.
This “abnormal” behavior of small fish is a mystery. Over the years, biologists have tried to unravel this phenomenon. Modern scientists believe that whales can guess the behavior of fish. In just a few million years, they learned to use a rare in the natural ratio between the size of the predator and the prey. Research results are published in the scientific publication PNAS.
Biologists experimented with some sea slaves. They demonstrated the image of a close predator. For this, volumetric dark spots of the right size were artificially created.Then scientists monitored the behavior of small fish. The data obtained were used for electronic modeling of the behavior of a group of fish in the conditions of approaching large natural enemies.
It turned out that small fish effectively responded to a change in the artificial spot, characteristic of an approaching predator not as large as a humpback whale. The most effective collective protection against a sea lion. It is for protection from predators of this size that the behavior of anchovies is most adapted. And when they see medium-sized predators, they run away from him in all directions.
During the modeling of the humpback whale attack, the growth of the artificially shaped figure was very slow. And this slow increase weakly scared the anchovies. Therefore, they did not run away until the mouth of a large whale was opened before them.
The same behavior was observed in the wild. A team of biologists observed the behavior of schools of fish near the southern California coast. Under natural conditions, the fish did not notice the slow approaching whale, which for a long time it seemed to them as a small spot. They began to get scared and run away only at the time when the huge whale came close to the fish and opened its big mouth. Since it was too late to run away from the predator, he managed to swallow up to two thirds of all the fish in the school.
