Animals

Sharks: How do they choose a partner and reproduce?

The sharks they have mating habits that are not yet completely clear to science, because in several species the sexual union takes place in the deep>

In captivity, these fish rarely reproduce as they do in the natural environment.

Shark Reproductive Strategy

From different perspectives there are several ways of carrying out reproduction, all with the same purpose, to perpetuate the species. Sharks are the great fish of the seas and oceans and, together, they form a group of more than 100 species, each with a different breeding strategy but can be encompassed in three different types:

Oviparous sharks

The oviparity is the reproductive strategy by which the animals lay eggs. In oviparous shark species, fertilized eggs are encapsulated in an egg box and deposited in the external environment. All the nutrients that the embryo will require are inside this egg capsule. No species of pelagic shark, that is, living free in the ocean away from the coast, are oviparous.

Ovoviviparous sharks aplacementarian with oophagy

The sharks of the lamniform order such as the fox shark or the salmon shark, exhibit aplacental viviparity with oophagy embryonic This means that they are ovoviviparous animals, the development of the embryo occurs within the mother's womb but in a very different way than a placental mammal would. In this case, only the right ovary is functional. After the intercourse occurs and the eggs are fertilized, they are individually packaged in capsules, called blastodisc capsules. These capsules migrate to the uterus (two), where development takes place.

In the first phase of pregnancy, the embryos feed on the yolk of the yolk sac that is inside the capsule. Once the yolk has been depleted, the embryos leave the capsule by swallowing it and, during this phase, they feed on the ovules (oophagy) unfertilized that the mother has continued to produce during pregnancy. The consumption of these nutritious capsules causes embryonic stomachs to become distended, which is why they are often referred to as "yolk stomachs."

Towards the end of pregnancy, the female stops producing eggs and late-stage embryos depend on the digestion of the yolk in the stomach for energy until birth. Being aplacementarian It means that there is no placental connection between fetuses and the mother in these species. White shark reproduction is poorly understood, but the few data that exist indicate that you should follow this reproductive strategy.

Placental ovoviviparous sharks

Sharks of the Carchariniform Order, specifically of the genera Carcharhinus Y Prionace they are all species placental viviparous. As in the previous case, the only functional ovary produces eggs that once they are fertilized are encapsulated in individual eggs and migrate to the uterus where development will occur. At the beginning of development, the embryos feed on the yolk stored in the egg but, when it is depleted, the empty yolk sac forms a placenta-like connection with the maternal uterine wall, which becomes highly vascularized (appearance of a multitude of blood vessels.

This "pseudoplacenta" is different from the placenta of placental mammals, but it functions as a true placenta, providing an exchange of nutrients and probably gases between the maternal and fetal systems. The embryos will depend on this placenta to overcome the final stage of development within the mother's womb. Just before birth, this connection is broken and small sharks reabsorb the rest of the bag. Newborns will have a small belly button scar.

Shark reproduction

As you will have seen, the reproduction of these animals is very different between the different species, therefore, the times in shark gestation will also be different, in fact, some do not even have a gestation period, since being oviparous the development of the embryos will take place outside the mother's body.

For sharks that are ovoviviparous, gestation time varies between 9 and 22 months, depending on the species, they could even reach 24 months of gestation. These data are not accurate, because studying these animals in their natural environment is certainly complicated.

It is also not known whether there is a specific reproduction or heat period for each species, although the data collected so far indicate that can be played at any time of the year.

In this video you can observe the mating ritual and the copulation of whitetip sharks:

How to differentiate a male and female shark?

The sexual maturity of sharks is reached when the reproductive organs are fully developed, something that is not appreciable from the outside, therefore, to know if an individual is an adult or we should not look at its size which, of course, varies by species.

For example, sexual maturity in males of Alopias superciliosus or fox shark is reached when the animal measures between 270 and 288 centimeters, this size corresponds to the age of 9 or 10 years. Females reach sexual maturity when they measure between 300 and 355 centimeters, that is, when they are between 12 and 13 years old old.

To know if a shark is male or female with the naked eye, we must look at the sewer area or anal area In fish, both the reproductive, urinary and excretory system pour their fluids into the sewer and from there to the outside. In females, next to the sewer we will see the cloacal fins (If the species has them, if not, we will only appreciate a small opening).

The males, on both sides of the sewer, have an appendix called pterygopodium. These appendices, inside have an organ called siphon It is filled with water before intercourse and will be emptied next to the sperm inside the female.

In the image below we can see a) Female sex organ (or sewer) of the shark, b) Male sex organ (or claspers), c) Shark in the neonatal stage with the umbilical opening open, d) Youth shark of the year with the umbilical hole partially closed

If you want to read more articles similar to How do sharks reproduce?, we recommend that you enter our Curiosities section of the animal world.

How to stand out from the crowd?

Dance or jump? Mobulas stripes meet in the dark to feed before the sun rises. Up to a quarter of a million copies can be concentrated in a single bank in search of a partner. It is believed that the more spectacular the jump, the stronger they impact on the water and better skills as a couple exist. In the video you can see how the stripes are displayed in their unique courtship. (Video: 'Shark', BBC Earth)

How is the courtship ritual? We Dance?

Hammerhead sharks star in a particular dance when they want to find a partner. They go to the dance to swim together in formation, the males outside and the females in the center. Males choose the largest females and go swimming together. At dusk, each couple disappears to mate. (Photo: Barry Peters)

Seduction or wrestling?

The intercourse is not always an elegant ritual. Male whitetip sharks are organized in groups to stalk a female. They immobilize her by biting her pectoral fin: At that moment they stop swimming and collide with the bottom. Mating begins that should last as short as possible, since during this process the male cannot breathe while holding the female's fin with his mouth. The video shows this aggressive and strenuous reproductive ritual.

Did you already know how sharks are born?

Once the male's semen has been introduced into the female, the role of the male shark ends. The female will ensure that the embryos formed reach term. It has also been seen that a litter of 32 pups had been bred from four different males so it is not uncommon to see multiple inseminations between sharks.

We explain the curious way of being born that sharks have. Source: Pixabay

The gestation of a shark varies greatly from one species to another and can last between 6 and 24 months. For example, the gestation of the Mielga shark is one of the longest, and not only among sharks, it really is the longest gestation period among vertebrates, as it can last up to 2 years.

But let's focus on what we have started: How are sharks born? Well, these can be born basically in three different ways: depending on whether they are oviparous, viviparous or ovoviviparous.

Approximately one third of shark species are oviparous and lay eggs.. In this case, the females have to hide the eggs in the sea, among the rocks, to avoid being eaten by predators. The embryos feed on the food that the egg contains for its development and the female only incubates the eggs until birth but no longer intervenes.

Sharks have three different ways to reproduce

Viviparous sharks are the ones that give birth to their young, that is to say, they have a period of gestation of the embryo, after which the birth of the shark takes place, in much the same way as mammals do. After fertilization, when the embryo has formed, it creates a bond with the mother and the placenta is formed, through which all embryos are nourished and developed. In fact, some females secrete what is known as uterine milk, a substance that is released in the yolk sac and that serves to nourish the fetus.

This type of reproduction is considered the most advanced that exists in the animal world and in the case of sharks, those that are viviparous usually belong to the largest species, such as blue sharks or hammerhead sharks. Approximately one third of shark species are viviparous.

Do you want to know what the spectacular birth of a shark is like? Source: Pixabay

But sharks have another peculiar way of being born, and that is what is known as ovoviviparous reproduction. In this case, females lay eggs, but instead of incubating them outside their body, as would be the case with oviparous animals, they incubate them inside. So in this case we also talk about the gestation period.

When the egg hatches, it does so inside the female and the baby continues to develop inside her mother, nourishing herself with the uterine milk she secretes. In this case there is no placenta, so there is no direct connection between the embryo and the mother. That's why sometimes ovoviviparity is also known as aplacental viviparity.

Sharks can be viviparous, oviparous and ovoviviparous

You may have heard that shark pups eat their siblings inside the mother's womb during pregnancy. This only occurs among ovoviviparous species and is called intrauterine cannibalism. It occurs when embryos have spent all the nutrients in their egg and need more food to stay alive. Sometimes they do not eat their siblings, but simply eat the food of other unfertilized eggs that are also found inside the female's uterus.

One of the most famous species in which this phenomenon occurs, is the bull shark. In this case, the female has two wombs and although she lays many eggs in each one, only two young are born. When the embryos develop, so do their teeth and when the nutrients provided by the egg run out, the shark pups eat the rest of the embryos in the uterus, as well as the unfertilized eggs. In this type of reproduction, the young are already born very large and very developed, being able to reach the meter in length.

Shark pups are independent at birth

The number of sharks that can be born in each litter varies greatly depending on the species to which they belong. In the case of the Bull shark, as we have already told you, only one or two sharks are born. But for example, in the case of the whale shark, the birth of 300 pups has been registered, although it is not usual. Blue sharks are viviparous and can give birth to hundreds of young in the same birth. Anyway I get to the world, offspring are a miniature version of sharks that will become.

Shark pups at birth are already completely independent. Immediately they are born and begin to swim away from their mothers. So they have to manage to find food and avoid predators. The survival success of shark pups depends, above all, on their size at birth. In addition, the area that the female has chosen to lay the eggs is very important.

Well we hope you enjoyed learning how sharks are born. As always, we are in the comments to answer any questions you may have>

Shark mating forms

In all shark species the courtship rules are the same. However, in general, when shark females enter the stage of sexual maturity, they produce pheromones or hormonal substances that are very attractive to males. These pheromones or chemical substances float in the sea and are different between species.

When the males attend the hormonal message, they swim in a circle again and again around the female. If there are several suitors, it can be decided who will mate with the female after defining who is the strongest. After the fight, the strongest male nibbles at the female to indicate that she is ready to mate. These bites are not dangerous, because the skin is thick enough to imply a risk.

The males do not have penises, but they have two clamps (CLASPER) on both sides of the body, through which the sperm is introduced. When they get pregnant, the females look for where to give birth to their young, or somewhere to lay their eggs.

After the birth of sharks, small newborns show their predatory instinct. They do not need their mother and have everything they need to defend themselves and get food.

Types of reproduction in sharks

Like most fish, sharks have an ovoviviparous reproduction (ovoviviparity), so the eggs are kept inside the female until they hatch and feed on the yolk of the egg and some fluids produced by the mother.

In some shark species, the young are born alive (viviparity), so they do not come through eggs. These little sharks are called puppies and, after childbirth, they are born perfectly adapted to survive without the need of their mother, who completely disregards them.

There is also another way in which sharks of certain species are born: by oviparity. The female leaves the sacks with eggs in hidden areas, out of reach of predators. In these bags there can be up to 100 eggs.

Cannibalism or zoophagy has been documented among sharks that have emerged from the eggs and eat those that are still in formation.

In captivity, some shark females have managed to reproduce asexually, that is, without the need of a male. Apparently, in the absence of a couple that fertilizes them, females have developed mechanisms to ensure survival in extreme conditions, which gives an idea of ​​the strong instinct of these fish.