Sharks have a different approach to reproduction than most fish species. Instead of releasing eggs and sperm into the water in an act of external fertilization, sharks go to great lengths to perform internal fertilization.
This isn’t a particularly easy feat when you’re swimming in the sea, but sharks have developed effective ways of overcoming these challenges.
Rather than holding onto one another in a warm embrace, the male shark bites the female, using his teeth to secure him in position.
This may not sound like a particularly romantic experience for either party, but it is effective and apparently causes the female shark little pain or discomfort, despite the telltale wounds the males leave behind.
How Do Sharks Mate?
Most shark species mate through internal fertilization, during which the male shark inserts one of its claspers into the female shark’s cloaca.
Male shark claspers behave in a similar way to a penis but are not independent appendages. Instead, they are extensions of the male’s pelvic fins that, in a great white, measure approximately “5–7 cm in diameter.”
Each clasper has a “dentine-covered spur or claw” that locks and holds the clasper in place inside the female’s body.
Do Sharks Mate Violently?
This method of reproduction sounds more horrific by the minute! First, the female shark endures bites to her fins, back, and flanks, and then she has a clasper jammed into her and held there by a sharp claw!
Fortunately, the female shark has thicker skin to protect them and, according to shark biologist Dr. Neil Hammerschlag, lack the “sensory receptors (known as nociceptors) responsible for feeling pain in humans and other mammals.”
As a result, a shark’s “response to injury is more of a reflex than a reaction to ‘pain’.”
Shark sex is still brutal, and researchers even use bite marks to distinguish female sharks from males.
What does Shark Mating Look Like?
Very few people have ever witnessed shark mating, although there are a handful of shark sex videos available on YouTube if you’re interested.
Videos like this one demonstrate how difficult it is for the mating couple to get into the right position and maintain it long enough to perform the deed.
Female nurse sharks make the mating process even more complicated by rejecting or blocking potential suitors. Only when they “flare and cup their pelvic fins” are female nurse sharks ready to accept the male’s advances, which can be complex in themselves.
Basking sharks are usually slow-moving creatures, but when they propel themselves out of the water and leap into the air, they reach speeds of around 18 kph.
Researchers concluded that the only reason for basking sharks to exert themselves in this way would be as a form of shark mating behavior.
They suggest that breaching is possibly a form of “male-male competitive behavior during courtship displays” and that female sharks may also breach “to signal their readiness for mating.”
Hammerhead sharks also perform complex mating rituals involving large schools of females that arrange themselves according to size.
In most species of sharks, the males simply shadow the females, swimming as close to them as possible. The females are thought to release “chemical signals, or pheromones,” to let the males know they’re ready to mate.
After some synchronized swimming, male sharks will attempt to bite the female to secure themselves in position. Although these are less severe than feeding bites, they still leave distinct bite marks on the female shark’s flanks and fins.
Once in position, the mating pair engage in a lot of rolling around and thrashing as the mating occurs.
After mating, the male and female sharks will often swim away into the sunset together but will usually part ways soon after. There’s little love lost in the world of sharks.
How Do Sharks Reproduce?
There are over 500 different species of sharks, all of which practice internal fertilization, but they don’t all reproduce the same way.
Oviparity
Some sharks lay eggs, burying them in the sand or mud at the bottom of the ocean, or securing them to a coral reef with tendrils. Once these oviparous sharks deposit eggs, their parental duties are over.
The water surrounding the egg case, or “mermaid’s purse,” delivers oxygen to the developing embryos, sustaining them until it’s time to hatch.
The only oviparous sharks known to perform any active parenting are Port Jackson sharks, and horn sharks. They carry their egg in their mouth to protect them from predators before screwing them into rock crevices to anchor them in place.
Aplacental Viviparity
Being abandoned in the ocean may sound dangerous, but it’s potentially safer than hatching inside the mother’s uterus, which is what happens in ovoviviparous sharks.
Sand tiger sharks, great white sharks, and nurse sharks are all ovoviviparous, which means they produce eggs but develop them inside the female’s body rather than externally.
The embryos are nourished by the yolk supply inside the egg until they hatch, at which point they turn to other means to get their sustenance. Many shark species practice oophagy, feeding off the unfertilized eggs in the mother’s wombs.
Others, like the sand tiger shark, have a rather more violent start to life. Turning on their smaller siblings, sand tiger babies eat the competition until there’s just one juvenile left in each of the mother’s uteruses.
Such intrauterine cannibalism ensures only the fittest and largest embryos survive, giving them a higher chance of surviving after birth.
Placental Viviparity
Viviparous sharks include the blue shark, bull sharks, and all species of hammerhead sharks. Like ovoviviparous species, they lay eggs inside their uteruses, but when these embryos hatch, they are nourished via “a placental connection similar to a mammal’s umbilical cord.”
When born, the baby sharks even have a small scar similar to a belly button, but it soon heals and vanishes from sight.
The gestation period for viviparous sharks varies widely, with some giving birth after just seven months and others taking years. However, it’s a species of ovoviviparous shark that has the longest gestation period.
The common frilled shark nurtures its embryos for three and a half years before giving birth, making the 5-month gestation period of the bonnethead look comparatively easy.
Parthenogenesis
Not only do bonnethead sharks have the shortest gestation period, but they’re also one of the few shark species that can reproduce without a mate. Through a process known as “automictic parthenogenesis,” a female shark produces not only the shark eggs but “three other products called polar bodies.”
When one of these polar bodies contains the same amount of genetic material as the egg, it can fertilize it without any sperm.
Although relatively common among invertebrate species, parthenogenesis is “exceedingly rare among vertebrate species,” and scientists have yet to understand the mechanism. They believe an absence of male sharks may trigger parthenogenesis, but beyond that, have little idea of why it occurs.
In March this year, a female smoothhound shark gave birth to a single pup at the Cala Gonone Aquarium in Sardinia. As there were no males in the tank, the only explanation is parthenogenesis.
This isn’t the first time a female shark’s given birth without any possibility of internal fertilization. In 2007, a bonnethead shark that hadn’t been near a male in over three years gave birth to a pup at the Henry Doorly Zoo in Nebraska.
Initially, researchers thought she may have stored sperm from a previous mating event, but DNA testing proved that the pup had “no paternal DNA,” and only “half of its mother’s genetic diversity.”
Although that means the pup is more closely related to its mother than a normal baby shark, it isn’t a replica or clone.
Unfortunately, the lack of genetic diversity means that pups born through parthenogenesis are “genetically disadvantaged” and may not survive to adulthood.
Interesting Shark Mating Facts
Do Sharks Give Parental Care?
Regardless of how juvenile sharks come into being, once born, they’re on their own. All sharks are both live and free-swimming and immediately separate from their mothers. This behavior serves to protect the juveniles that would otherwise become potential prey for their hungry mothers.
Many juvenile sharks take refuge in shark nurseries, where shallow waters protect them against larger predators, and an abundance of food encourages them to practice their hunting skills.
Some species of sharks, including lemon sharks, remain in these nursery areas for up to four years. Only once they’re big enough to fend off the cannibalistic approaches of adult lemon sharks do they venture into the open sea.
It appears the maternal instinct isn’t a factor in shark mating, but some marine biologists and psychologists disagree.
According to the author Gay Bradshaw, “sharks feel love and emotions as much as we do,” even though they don’t express them in the same way. For the shark babies, it’s clearly a case of tough love, rather than motherly love!
Where Do Sharks Mate?
Scientists believe that some species of sharks migrate huge distances to find a mate. For example, although there are only two metapopulations of whale sharks in the world, one in the Indo-Pacific and the other in the Atlantic, the two groups appear to “swap genes.”
It seems the two groups come together to mate before the females head off thousands of kilometers into the ocean to give birth.
Other shark species also congregate in specific areas for mating. Large groups of hammerhead sharks gather off the coast of Layang Layang, some 300 km from the coast of Borneo, while OCEARCH shark scientists suspect that great whites assemble off the Carolinas to find their love match.
Some shark species return to the same place year after year to mate and give birth. Nurse sharks loyally return to Florida’s Dry Tortugas National Park to mate every year, with studies indicating that some individuals keep returning for a “period of up to 28 years.”
Female Sharks Can Store Sperm
Although some species are loyal, like the nurse shark, others don’t need to mate every time they want to become pregnant. Some shark species can store a male’s sperm for months, if not years, fertilizing further eggs when necessary.
Bamboo sharks have been known to store sperm for up to four years before giving birth, a fact that would cast doubt on the concept of parthenogenesis if it weren’t for the DNA evidence.
Researchers like Adele Dutilloy believe this may “be a strategy to reduce the need for more frequent mating events.” Seeing as shark mating is aggressive and potentially harmful to the females, you can understand why they might want to avoid it!
This practice seems to be more common among deep-sea shark species, like the longnose velvet dogfish and leafscale gulper shark, whose populations are small and widely dispersed, limiting their mating opportunities.
Conclusion
Although all sharks use internal fertilization to reproduce, there’s where the similarities end. Some sharks lay eggs externally, while others hatch them inside their uteruses and start hunting before they’re even born.
Sharks have been swimming in our seas for millions of years, which has given them plenty of time to diversify. Some female sharks can even store sperm for later use or fertilize their own eggs without any male present.
These adaptations help protect the species and ensure its survival, but the shark’s complex reproductive cycle could be jeopardizing its future.
Sharks take a long time to mature, give birth to small litters of pups, and often have long gestation periods. These factors make it challenging for an individual species to recover, especially if it’s being hunted by humans.
As climate change and pollution make an increasing number of shark nursery areas unviable, so the challenges to our global shark populations are increasing.
A better understanding of the behavior and mating habits of different shark species can help us to understand the impact climate change and commercial fishing operations are having on our marine predators and could enable us to develop more effective ways of protecting and conserving our sharks for the future.
Nicky is a British adventurer and animal lover who spends her time exploring the natural world and writing about her experiences. Whether on horseback, underwater, running, hiking or just standing with a fishing rod in hand, she embraces everything her adopted home of South Africa has to offer.