Sharks are often perceived as ferocious creatures; in essence, they’re just another vital part of the ocean’s fragile ecosystem.
At the apex of the food chain, they keep the population of other species in check and maintain balance. But, do sharks lay eggs or give live birth when it comes to reproduction?
Surprisingly, sharks have a variety of reproductive strategies that enable them to cope with various environmental conditions. Researchers report that 40% of approximately 500 shark species lay eggs, while the rest give live birth.
Table of Contents
Do Sharks Lay Eggs?
As previously mentioned, egg-laying (oviparity) is one of the most common shark reproduction methods, accounting for around 40% of all species.
The eggs are fertilized internally and laid in a mermaid’s purse, a protective case that keeps the eggs safe while the embryo develops. The egg case may attach to the ocean floor or wash up on shore.
During the gestation period, which can last several months, the embryo receives nourishment from its yolk sac. But in some situations, the egg may remain inside the female for some time. This enables the shark embryo to develop and increases its chances of surviving outside the mother’s body.
However, most shark species give birth to live young, with their embryos receiving nourishment while still in the mother. They are known as viviparous sharks and are further classified as follows:
Ovoviviparity
Ovoviviparity occurs when the eggs hatch within the mother’s womb but receive nourishment from the yolk sac. As a result, the mother shark gives birth to fully developed but miniature sharks.
Some examples of ovoviviparous sharks are tiger sharks, whale sharks, dogfish sharks, thresher sharks, basking sharks, and angel sharks.
Viviparity
Similar to mammals, the shark embryos are attached to their mother’s uterine wall by an egg yolk sac placenta, through which nutrients are delivered.
However, this type of reproduction is uncommon, constituting about 10% of shark species, especially among the larger ones. Hammerhead sharks, bull sharks, and lemon sharks fall into this category.
Oophagy and Embryophagy
Unlike the other two reproduction techniques, shark pups obtain nourishment by feeding on their unborn siblings (Embryophagy) or unfertilized eggs (Oophagy) instead of a yolk sac. Oophagous sharks include sand tigers, shortfin mako, and white sharks.
What Shark Species Lay Eggs?
Oviparous is the term for the 40% of sharks that lay eggs. Once fertilized, the eggs are laid in an egg case called a mermaid’s purse to safeguard them while they develop into baby sharks.
The yolk sac nourishes the embryos during the gestation period until they hatch.
Some examples of oviparous species include:
Carpet Sharks
Although commonly found in the Indo-Pacific region, you can find this type of shark in all oceans worldwide. They have five gills, two dorsal fins, and a small mouth opening. Some lay eggs without a mermaid’s purse.
Bamboo Sharks
Whitespotted bamboo sharks mainly dwell in the Pacific Ocean from Japan to Indonesia and Madagascar, with a concentration in coral reefs. They are relatively small, about 37 inches in length, and lay a 5-inch length egg that incubates between 14 and 15 weeks.
Bullhead Sharks
Bullhead sharks prefer warm, tropical water and are distinguished by their back-and-forth swimming motion. The eggs are often oval but slightly pointed.
What Is a Mermaid Purse?
A mermaid purse is a tough shell that surrounds the egg and protects the shark embryo during incubation. Apart from oviparity sharks, skates are the only other species with mermaid purses. You can easily see them on the beach, or tidal lines, particularly during strong currents or storms.
They are often mistaken for washed-up air bladders of seaweed at first glance due to their brown and black color. However, a closer inspection reveals distinctive curled or spikey strands on either side and a leathery texture.
The strands are known as tendrils, and they anchor the purse to the ocean floor, corals or seaweed so that it doesn’t drift away with the current.
What Are Spiral Shark Eggs?
They are eggs laid by female Bullhead and Horn sharks and have an auger-like case with two curling tendrils at the bottom. The spiraled case allows the mother to wedge the egg into the rocky crevices of the sea floor, keeping it safe from predators until it hatches.
What Species of Sharks Give Live Birth?
Viviparous are shark species that give live birth to their young rather than lay eggs. Their embryo receives nourishment and develops within the mother’s uterus until they’re born, usually after a 9–12 month gestation period.
Species of viviparous sharks include:
Lemon Sharks
Lemon sharks dwell mainly in subtropical shallow water but usually return to nursery grounds for breeding. You can identify Lemon sharks by their two dorsal fins, flattened head, and broad snout.
Tiger Sharks
The Tiger shark’s largest population is in temperate and tropical waters and is characterized by dark stripes resembling tiger markings.
White Sharks
Named for their white underbelly, this apex predator can grow up to 20 feet long and weigh 4,200-5,000 pounds for females. It can live for up to 70 years, and you can find it on all seas’ coastal shelves.
Generally, viviparous sharks (lemon, tiger, and white) give live birth rather than laying eggs.
Do Sharks Nurse Their Pups?
Sharks do not nurse their pups. However, they ensure they’re delivered in safe habitats along the shore, seamounts, and estuaries with abundant, easy prey.
Can Shark Pups Eat Each Other?
Shark pups devour their siblings inside their mothers’ wombs, a phenomenon known as intrauterine cannibalism. This makes them bigger and stronger, increasing their chances of survival after birth. It is also a paternity contest, with puppies from various male sharks striving to be born.
How Do Sharks Mate?
Sharks reproduce predominantly through internal fertilization, which happens in the spring and summer.
When a female shark is ready to mate, it emits a pheromone that the male can detect. The male approaches and a lot of biting ensues between the two before mating occurs.
Often, the male bites the female’s dorsal fin with his teeth to stabilize her before inserting one of his claspers into the female’s oviduct and releasing sperm.
Can Sharks Reproduce Without Mating?
Sharks may reproduce asexually, especially when males are scarce. This rare phenomenon is known as parthenogenesis and occurs when a female egg fuses with a polar body that fertilizes it rather than a sperm cell.
However, this type of reproduction leads to weaker offspring due to a lack of genetic variation.
Wrapping Up
Sharks play a vital role in the marine ecosystem, and their reproduction ability is critical. Two of their most common reproductive strategies are oviparity (egg-laying) and viviparity (live birth). So, the answer to the question “Do sharks lay eggs?” is yes, but only 40% of shark species do so.
Add comment