Is it true that sharks feel blood in water per kilometer?

Often, people who are resting near the habitats of sharks do not go into the water, if there is even a small scratch on the body. All due to the widespread belief that even one drop of blood will attract a predator floating per kilometer. We checked whether these fears are justified.

Although from the attack of sharks per year Dying On average, only five or six people, the stereotypes established in decades and the frightening look of predators affect the consciousness of people much stronger than not so frightening statistics. The fear of sharks and their olfactory abilities are also reflected in the popular culture - for example, in the cartoon “In Search of Nemo”, so -smiled blood returned the animal instincts and Overwhelmed Shark adhere to the rule "Fish is a friend, not food." In English, there is even an idiom to smell Blood (literally “smel up blood”), meaning “Detect the vulnerability of the opponent” and appeared including thanks to sharks.

Sharks really have an extremely developed scurry. Unlike people, they have no respiration and sense of smell: these animals receive oxygen through gills, and information about the smells through the nostrils on the muzzle. In this way, the body is arranged in other fish, but the nasal cavity of sharks is filled with a large number of receptors, thanks to which you can distinguish a huge palette of smells.

Based on this premise, researchers from the Atlantic University of Florida We decided to check, is the smell of sharks so developed to smell a drop of blood at a great distance. Biologists have chosen for the experiment of rhombo and tailing slopes, as well as lemon and ground -headed sharks - all these species are included in the subclass of the plately -ghost. Each animal was placed in a container of water, and a dispenser was brought to the nose that produces different amino acids, and an electrode that measured activity in the cavity with olfactory receptors.

As the researchers found out, the shark's smell is not much different from their brothers. The maximum concentration, at which the animals managed to distinguish the amino acid in water - about 1 to a billion. As biologists explain, this is several orders of magnitude higher than in the case when a drop of blood enters the ocean at a distance of a kilometer from the shark. The results did not become amazing for scientists, because a higher sensitivity would simply have drowned out predators crazy - then they would literally feel all the smells and could not distinguish between them really important.

A similar experiment Spent Science popularizer and blogger Mark Robert. He went out in a boat in the open sea, where many sharks live, and placed four surfing boards at an equal distance from it. On each of these boards, the experimenter put a container with one of the four liquids: cow blood, human urine, fish oil and sea water (as a control). With the help of special devices, the tanks were evenly devastated, and Robert counted how many sharks different liquids would attract. In an hour, the board with which fish oil was supplied to the water attracted four sharks, a boat with blood - 41, and the other two were ignored.

After making sure that the blood really interested in animals, Robert wondered: what number is enough for this. This time, the experimenter filled two containers on two with human blood boards, which he drove into the water at different speeds: from one board - one drop every minute, on the other - one drop every four seconds. Another capacity, as in the first experiment, was filled with sea water for control. This time, none of the boards attracted the attention of sharks. “No one was interested in a device that produces 15 drops of human blood per minute in the midst of water sharks. Perhaps everything will be fine with you in the case of a small scratch, ”Robert summed up.

Not true

What do our verdicts mean?

Read on the topic:

1. https://jeb.biologists.org/content/jexbio/213/20/3449.Full.pdf
2. https://www.popmech.ru/science/11003-zhazhda-krovi-razvenchanie-akul/