Is the fame of the great white shark justified?

If there is an animal about which there is a black legend, then this is the white shark.

Carcharodon karharias (that’s what it is called taxonomically) is a Quaternary consumer or top predator. This means that it is at the highest level of the food chain, including other predators in its diet, a trait it shares with other “predators” such as eagles, polar bears, or killer whales. However, it is the big white that tops the pedestal of the scariest species. A great movie is to blame for this. Jaws (dubbed in Spanish as Shark), from no less brilliant director Steven Spielberg.

The question is, does this species really deserve such awesome fame?

sharks sixth sense

Sharks constitute an evolutionarily very homogeneous group and have the oldest origin among vertebrates. In the Cretaceous period (Mesozoic era) there were already representatives of almost all groups. This means that they survived for millions of years, successfully competing with much more modern fish, possessing completely unique anatomical and physiological features.

Everyone knows the multi-row arrangement of their teeth, as well as their extraordinary olfactory sensitivity. His way of extending his jaws when attacking is also vox populi, made possible by the fact that his upper jaw (palatosquare cartilage) is not welded to the skull.

But perhaps their exclusive Lorenzini ampoules are not so popular. This is the sixth meaning (in the literal interpretation of the term), opening outwards with many pores, especially distinguishable on the head. With them, by playing with the concentrations of calcium and potassium in a very specific and adaptive way, they manage to detect something unimaginable to us: electromagnetic fields.

They use this sense to communicate during social and reproductive interactions. And, most interestingly, with its help they detect prey, even if it is visually camouflaged, remains motionless or does not emit any smell. Since their detection threshold is very low (on the order of 5 nanovolts/cm), they detect prey simply by electrically changing its heartbeat.

To top it off, the ampullae of Lorenzini function as endogenous compasses, constantly providing orientation. Recall that our planet, thanks to its iron core, is a giant dipole. seláceos, which detect the generated magnetic fields, always have clear main reference points.

Thus, we have a group of animals that navigate and detect prey or enemies better than any of our very modern boats equipped with sonar, radar and GPS. Marvelous.

Pretty special shark

Everything we have discovered so far is characteristic of all elasmobranchs, from the great whale shark to the humblest of cat sharks, passing through the also fearsome great whites (Karharin), tiger sharks (Galeocerdo) or hammerhead sharks (Sphyrna). However, the glory goes to the white shark. Cause?

First of all, it belongs to the lamnid family, a select club of five living species that are unusually hydrodynamic, strong, compact, fast, large and have strongly developed teeth. Of all of them Carcharodon karharias This is one that can reach large sizes. And of course, when it comes to loot, size matters.

Avoiding all unofficially confirmed white records over 7 meters, the largest objective size corresponds to a female with a total length of 6.3 meters and a weight of 1.6 tons. Interesting, especially when it comes to hunting species, which, in turn, are predators, that is, they can use their “weapon” for your own protection.

On the other hand, the large jagged triangles that form the rows of its teeth and are oriented in several directions at the same time are effective systems for capturing and killing animals the size of sea lions.

fat management

It’s not about that. The white shark has an ace up its sleeve to make the predatory process profitable. Before explaining it, it must be remembered that, unlike bears or killer whales, we are talking about fish, that is, poikilotherm or “cold-blooded animal.” This means that your physiology will not allow you to heat up what you eat.

This is important because, in order to be processed, fats must be in a liquid state, that is, they must “melt”. When you eat a good chorizo ​​or a slice of bread and butter, your own body heat from a warm-blooded animal causes the fatty part of what you eat to melt in your stomach. So you can emulsify them with bile salts (which enter the duodenum from the common bile duct) and once digested, your intestines can absorb the needed caloric fatty acids.

The white shark, in principle, could not carry out this process, so the tasty and fat seal, which she just had a snack, will be of little use in terms of energy. But evolution has endowed it with a spectacular mechanism: look back extraordinarily developed. This is a complex network of arterioles and venules, very close to each other, which, through a system of countercurrents, provides two very interesting local effects: an increase in the partial pressure of oxygen and an increase in temperature.

This prevents the shark’s metabolic heat from dissipating into the surrounding water, as fish normally do, causing their internal temperature to rise to 15ºC in certain anatomical areas. The consequences are more than beneficial: through cold water, he can increase the area of ​​u200bu200bits distribution, his muscles contract more efficiently and quickly, his brain processes information better, and his digestive system absorbs fat with efficiency unthinkable for fish.

In short, it is an extraordinary predator, not only because of its anatomy, but also because of the practical physiological homeothermy that allows it to hunt warm-blooded prey such as fast seals or agile pinnipeds efficiently and actively.

Therefore, his fame is well deserved. And you don’t need fake special effects. Mediocre filmmakers who tried to imitate the great Spielberg could rid a lungless animal of an unbearable tiger roar and therefore never make those “airy” sounds.

This article arose from the mentorship of Jesús Ponce Pérez, a student at UMA, on a graduation project.

A. Victoria de Andrés Fernández, Professor of Animal Biology at the University of Malaga

This article was originally published on The Conversation. Read the original.

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