Big-eyed fox shark — a predatory fish that lives at a depth of several hundred meters: it is accustomed to conditions of low light and low temperature. It is notable for its long tail, which it uses when hunting like a whip or a hammer, hitting its victims and stunning them. It is not dangerous for people, but people are dangerous for it – the population of the species is falling due to fishing.
Origin of the species and description
Photo: Bigeye fox shark
The species was described by R.T. Lowe in 1840 and was named Alopias superciliosus. Subsequently, Lowe's description was revised several times along with the place in the classification, which means that the scientific name also changed. But this is a rare case when the first description turned out to be the most correct, and exactly a century later the original name was restored.
Alopias is translated from Greek as “fox”, super from Latin “over”, and ciliosus – “eyebrow”. Fox – because since ancient times, sharks of this species were considered cunning, and the second part of the name was obtained because of one of the characteristic features – depressions above the eyes. The origin of the species dates back to the deepest antiquity: the first of the direct ancestors of sharks swam the earth's oceans back in the Silurian period. It was to that time that fish with a similar body structure belong, although it has not been established exactly which of them gave rise to sharks.
Video: Big-eyed fox shark
The first of the real sharks appear by the Triassic period and quickly achieve prosperity. Their structure is gradually changing, calcification of the vertebrae occurs, due to which they become stronger, and therefore faster and more maneuverable, and also gain the ability to settle at great depths.
Their brain grows – sensory areas appear in it, thanks to which the sense of smell of sharks becomes extraordinary, so that they begin to feel blood even when they are tens of kilometers from the source; the jaw bones are improved, making it possible to open the mouth wide. Gradually, during the Mesozoic, they become more and more like those sharks that live on the planet now. But the last significant impetus for their evolution is given by extinction at the end of the Mesozoic era, after which they become almost undivided masters of sea waters.
During all this time, the already ancient superorder of sharks continued to give rise to new species due to the ongoing changes in the environment. And bigeye sharks turned out to be one of the youngest species: they appeared only in the middle Miocene, this happened about 12-16 million years ago. Since that time, a large number of fossil remains of this species have been found, before that they were absent, representatives of the closely related pelagic fox shark appeared a little earlier – they descended from one common ancestor.
Appearance and Features
Photo: What the bigeye shark looks like fox shark
In length, adults grow up to 3.5-4, the largest specimen caught reached 4.9 m. They weigh 140-200 kg. Their body is spindle-shaped, the snout is sharp. The mouth is small, curved, there are a lot of teeth, about two dozen rows below and above: their number can vary from 19 to 24. The teeth themselves are sharp and large.
The most obvious sign of fox sharks: their tail the fin is extremely strongly elongated upward. Its length can be approximately equal to the length of the entire body of the fish, so this disproportion in comparison with other sharks will be immediately noticeable, and representatives of this species will not be confused with anyone else.
Also, as their name implies, they are distinguished by the fact that they have large eyes – their diameter can reach 10 cm, which is larger in relation to the size of the head than other sharks. Thanks to such large eyes, these sharks see well in the dark, where they spend most of their lives.
It is also noteworthy that the eyes are very elongated, due to which these sharks are able to look straight up without turning. On the skin of this fish, scales of two types alternate: large and small. Its color can be brown with a strong tinge of lilac or deep purple. It lasts only when alive, a dead shark quickly turns gray.
Where does the bigeye fox shark live?
Photo: Thresher shark in Turkey
Prefers waters of the tropics and subtropics, but also found in temperate latitudes.
Four main distribution areas can be distinguished:
- western Atlantic – from the coast of the United States, the Bahamas, Cuba and Haiti, along the coast of South America to the south of Brazil;
- the eastern Atlantic – near the islands, and further along Africa until Angola;
- The Pacific Ocean – from Korea along the coast of Asia to Australia, as well as some islands in Oceania. They are even found far to the east, near the Galapagos Islands and California.
west of the Indian Ocean – near South Africa and Mozambique to Somalia to the north;
As can be seen from the distribution range, they often live near the coast and can even come very close to the coast. But this does not mean that they live only near land, rather, more is known about just such individuals, but they are also found in the open ocean.
The optimal water temperature for these sharks is in the range of 7-14 ° C, but sometimes they swim to great depths – up to 500-700 m, where the water is colder – 2-5 ° C, and can stay there for a long time. They are not strongly attached to the habitat and can make migrations, but in their course they cover not too large distances: usually it is several hundred km, in rare cases 1,000 – 1,500 km.
Interesting fact: Thanks to an orbital vascular system called rete mirabile, these fish are able to withstand large fluctuations in water temperature: a drop of 14-16 ° C is completely normal for them.
Now you Do you know where the bigeye fox shark lives? Let's see what it eats.
What does the bigeye shark eat?
Photo: Red Book Bigeye Thresher Shark
On the regular menu of this species:
- mackerel;
- hake;
- squid;
- crabs.
They love mackerel very much – researchers even found the relationship between the mackerel population and these sharks. When there are fewer mackerels in some part of the ocean, you can expect that the bigeye shark population nearby will also decline over the next few years.
In the Mediterranean Sea, they often follow tuna schools for a long time, attacking them once or twice a day – so they do not need to constantly look for prey, because these schools are very large, and a few bigeye sharks can feed only on them for months, while most of the shoal still survives.
In the diet of some individuals, mackerel or tuna make up more than half – however, they also feed on other fish. Among it are both pelagic and bottom pitchforks – this shark hunts both in depth, where it usually lives, and closer to the surface.
They usually hunt in a pair or a small group of 3-6 individuals. This allows you to hunt much more efficiently, because several hunters at once introduce much more confusion and do not allow the victims to quickly figure out where they should swim at all, as a result of which they manage to catch much more prey.
This is where long tails come in handy: they are used by sharks to hit a school of fish and force prey to huddle tighter. By doing this from several sides at once, they get a very close group, and their victims are stunned by tail blows and stop trying to escape. After that, the sharks simply swim into the formed cluster and begin to devour the fish.
Character and lifestyle features
Photo: Bigeye Thresher Shark Underwater
They don’t like warm water, and therefore they spend the day under the thermocline – a layer of water, from which its temperature drops sharply. Usually it is located at a depth of 250-400 m, where sharks swim in water with a temperature of 5-12 ° C and feel great in such conditions, even low light does not bother them.
And at night, when it gets colder, they rise up – this is one of the rare species of sharks, which is characterized by diurnal migrations. In the dark, they can be seen even at the very surface of the water, although more often they swim at a depth of 50-100 m. It is at this time that they hunt, and during the day they mostly rest.
Of course, if prey meets them during the day, they can also have a bite, but much more active at night, it is at this time that they become merciless fast predators, capable of sharp jerks in pursuit of prey and unexpected turns. They can even jump out of the water if they are hunting near the surface. It is at such moments that the shark can get hooked, and usually clings to it with its tail fin, with which it hits the bait, trying to stun it. Like most other sharks, the bigeye has an excellent appetite and eats fish in very large quantities.
Greed is also inherent in her: if her stomach is already full, and there are still a lot of stunned fish swimming nearby, she can empty it to continue the meal. There are also cases of fights for prey both between bigeye sharks and sharks of other species: they are usually very bloody and end in severe injuries to one of the opponents, or even both.
Despite their bad temper, they are almost harmless to humans. Attacks of representatives of this species on people are not registered. They generally prefer to swim away if a person tries to get close, and therefore it is quite difficult to imagine a situation in which a person will suffer from their teeth. But in theory this is possible, because their teeth are large and sharp, so they can even bite off a limb.
Interesting fact: In English, fox sharks are called thresher shark, that is, ” thresher shark.” This name comes from their way of hunting.
Social Structure and Reproduction
Photo: Bigeye fox sharks
They live alone, They gather only for the time of hunting, as well as during breeding. It can happen in any season. During intrauterine development, the embryos first eat the yolk, and after the yolk sac is empty, they begin to eat unfertilized eggs. Other embryos are not eaten, unlike many other sharks.
It is not known how long the gestation lasts, but this shark is viviparous, that is, fry are born immediately, and there are not many of them – 2-4. Due to the small number of embryos, big-eyed sharks breed slowly, but there is a plus in this – the length of the sharks that have just been born is already quite impressive, it is 130-140 cm.
Thanks to this, newborns can almost immediately stand up for themselves, and they are not afraid of many predators that torment sharks of other species in the first days or weeks of life. Outwardly, they already strongly resemble an adult, except that the head looks larger in comparison with the body, and the eyes stand out even more than in adult sharks of this species.
Big-eyed sharks are even born already covered with rather dense scales that can serve as protection – therefore, the oviduct in females is covered from the inside by epithelial tissue, which protects it from damage by the sharp edges of these scales. In addition to the small number of sharks born at a time, there is another important problem in their reproduction: males reach sexual maturity by 10 years, and females a few years later. Given that they only live 15-20 years, this is very late, usually females have time to give birth 3-5 times.
Natural enemies of bigeye thresher sharks
Photo: Bigeye shark
Adult individuals have few enemies, but they do exist: first of all, these are sharks of other species, larger ones. They often attack “relatives” and kill it, in the same way, and any other fish, because for them it is the same prey. Bigeye sharks are able to avoid many of them due to their great speed and maneuverability, but not all of them.
At least vigilance, being close to a large shark, she has to show. This also applies to fellow tribesmen: they are also capable of attacking each other. This does not happen so often, and usually only with a fair difference in size: an adult may well try to bite a young one.
Killer whales are very dangerous for them: in a fight with these strong and fast predators, the big-eyed shark has no chance , so it remains only to retire, barely seeing the killer whale. The blue shark is a direct competitor of the bigeye for prey, so they do not settle nearby.
Sea lampreys do not pose a danger to an adult, but they are quite capable of defeating a growing one, and attack even at the same size. When they bite, they introduce an enzyme into the blood that prevents it from clotting, so that very quickly the victim begins to weaken due to blood loss, and becomes easy prey. In addition to large enemies, bigeye sharks and parasites such as tapeworms or copepods are pestering.
Population and species status
Photo: What a bigeye fox shark looks like
Throughout the 20th century, a decline in the population was noted, as a result of which the species was listed as vulnerable in the Red Book. This is the lowest degree of protection for the species, and it means that there are still not so few bigeye sharks on the planet, but if no action is taken, they will become less and less.
The problems of the species are due to first of all, its sensitivity to overfishing: due to low fecundity, even a catch in volumes that are moderate for other fish becomes a serious blow to the population of bigeye sharks. And they are commercially fished, they also act as one of the objects for sport fishing.
First of all, their fins are valued, used to make soup, liver fat, which is used to produce vitamins, and the skin. The meat is valued little because it is too soft, similar to porridge, and its taste properties are average at best. Nevertheless, it is also used: it is salted, dried, smoked.
These sharks are actively caught in Taiwan, Cuba, the USA, Brazil, Mexico, Japan and many other countries. Often they are caught as by-catch, and fishermen who catch completely different species do not like them very much, because with their fin they sometimes tear apart the nets.
Because of this, and also because of the fact that it is higher fins are most valued, previously there was a barbaric practice in which the fins of a bigeye shark caught as bycatch were cut off, and the carcass was thrown back into the sea – of course, it died. Now it has almost been eradicated, although in some places this practice is still practiced.
Bigeye fox shark protection
Photo: Bigeye fox shark from the Red Book
So far, measures to protect this species are clearly insufficient. This is due both to the fact that it is on the list of vulnerable ones, and they are protected mainly on a residual basis after those species whose threat is more acute, and to the fact that the inhabitants of the sea are generally more difficult to protect from poaching.
Among other things, there is the problem of the migration of these sharks: if in the waters of one state they are at least somehow protected, then in the waters of another, no protection may be provided for them at all. Still, over time, the list of countries taking measures to protect this species is getting longer.
In the United States, fishing is limited and it is forbidden to cut off the fins – the entire carcass of the caught shark must be used. It is often easier to let her go if she was caught as a by-catch than to comply with this prescription. In the European countries of the Mediterranean, there are bans on drift nets and some other fishing gear that cause great damage to bigeye sharks.
Interesting fact: Like many other sharks, bigeye foxes are able to do without food. This predator may not worry about food for weeks and even months. The stomach empties quickly, but after that the body switches to another source of energy – oil from the liver. Their liver itself is very large, and an unusually large amount of energy can be extracted from its oil.
This slow-growing and low-bearing bigeye fox shark is not able to withstand the pressure of a person: even despite the fact that fishing for it is not so active, its population is falling year after year. Therefore, additional measures are required to protect it, otherwise the species will be on the verge of extinction in a few decades.
