There are over 400 shark species alive today. Sharks make up an important part of the ocean ecosystem as primary predators. This places sharks at the top of the food chain, which means their presence controls the population size of species located further down the food chain. As a result, their ability to survive and reproduce affects all lifemaritime.

A shark's skeleton is composed of cartilage instead of bone. This unique feature places all sharks within the same family of fish. Despite belonging to the same family and sharing similar skeletons, shark species are characterized by a number of physical differences. One of the most notable differences between sharks is size. Some sharks are as large assmall as a few centimeters in length, while others can reach a length of over 9 meters. In fact, the largest fish species in the world is the whale shark, which grows up to 16 meters in length.

In general, sharks reach reproductive maturity between 12 and 15 years of age. Furthermore, they share similar reproductive behaviour in the practice of internal fertilisation. This fertilisation behaviour means that male sharks release sperm inside female sharks to fertilise eggs. Only 1 or 2 eggs are fertilised at a time, which contributes to slow growth andpopulation recovery.

The difference in shark reproductive behaviour is that some sharks give birth to live pups - these are known as viviparous. And other sharks lay eggs - these are known as oviparous.

Oviparous sharks

Researchers report that about 40% of all sharks in the world are oviparous, or egg-breeding. Shark eggs are protected by a special case, also known as a mermaid bag, when they are laid. Sometimes these egg cases have long strings hanging from them, which serve as an anchor and allow the egg case to attach to algae and coral on the bottom of the ocean floor. Inother cases, shark egg cases sink to the bottom of the ocean, where they rest under rocks or other debris from the ocean floor. The mermaid pouch is often slightly transparent, which allows you to observe the development of the embryo.

Shark eggs are filled with a yolk that serves as a source of nutrition for the developing shark. This extra nutrition during the embryonic development stage helps the shark to hatch to a high level of maturity, which works to ensure a greater chance of survival for the young hatchlings. The constitution of shark eggs is different from that of other shark eggs.fish, which are not composed of yolk. Baby turtles, also known as chicks, are therefore more independent at birth and do not require extra care. This independence means that adult life begins the moment they are born, when they start to swim, migrate, hunt and eventually reproduce.

Hatching time varies between shark species. In some cases the embryo relies on egg yolk as a food source in which case hatching can take several months. In other cases the egg is allowed to develop for longer while inside the parent shark and therefore the hatching time is shorter.

Which sharks lay eggs?

As mentioned earlier, 40% of all shark species lay eggs. Some of the many aviparous shark species include carpet sharks, bamboo sharks, zebra sharks and bullhead sharks.

Carpet sharks

Whitetip sharks inhabit all the world's oceans, although this species is mainly concentrated in the Indo-Pacific region. The term "whitetip shark" actually refers to a number of shark species that belong to the family Orectolobidae All carpet sharks have two dorsal fins, five gills and a small mouth opening. In this family of sharks, females lay eggs in a variety of methods. Some female carpet sharks lay eggs in the previously mentioned protective egg case, while others simply lay eggs without a protective case. Researchers have observed that in some cases the female worksto more fully protect the egg by pushing it between rocks on the bottom of the ocean floor in order to hide it from potential predators. Zebra sharks are included in this category. Some species of carpet sharks, however, have live births.

Bamboo sharks

Bamboo sharks, both the white-spotted and chestnut varieties, are also oviparous. The whitetip shark is relatively small, growing to only about 1 meter in length. This species can be found in the Pacific Ocean, where they are particularly concentrated around the coral reefs located within Indonesian waters. The female whitetip shark putsan egg that is about 10 centimeters long and takes between 14 and 15 weeks to hatch. Interestingly, researchers found that a captive female at the Belle Island Aquarium in the U.S. state of Michigan laid several eggs, three of which fully developed. This event occurred after she had been isolated from other males for about 6 years. The theories forexplain this anomaly include that bamboo sharks have both male and female organs, female bamboo sharks perform parthenogenesis (which is producing a fertilized egg without male organs), and female bamboo sharks can carry previously deposited sperm for long periods of time.

Bullhead sharks

Bullhead sharks are another egg-laying shark species. This type of shark is divided into 9 distinct species, all belonging to the fish family Heterodontidae All species of bullhead shark prefer to inhabit warm, tropical waters and forage along the ocean floor between areas of rocky reef. Mollusks, crustaceans and sea urchins make up the bulk of their diet. The largest of these species can reach lengths of up to 2 meters, while the smallest of these species reaches only 60 centimeters. The bullhead sharkbullhead shark is considered a relatively small shark species. Bullhead sharks are recognized by their swimming style, which is generally described as a kind of back-and-forth churning. The female bullhead shark lays slightly pointed oval-shaped eggs, which she pushes down between cracks in rocks on the ocean floor. This behavior serves toprotect the embryo, allowing its full development.

Do sharks lay eggs?

Learn Which Sharks Lay Eggs (thoughtco.com)