Do Sharks Lay Eggs?

Sharks Around the World

More than 400 shark species live throughout the oceans of the world. Sharks make up an important part of the ocean ecosystem as primary predators. This role 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 ocean wildlife.

A shark's skeleton is composed of cartilage rather than bone. This unique characteristic places all sharks within the same fish family. 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 among sharks is size. Some sharks are as small as a few inches in length, while others can reach a length of more than 30 feet. In fact, the largest fish species in the world is the whale shark, which grows to between 32 and 55 feet in length.

Shark Reproductive Behavior

In general, sharks reach reproductive maturity between the ages of 12 and 15 years. Additionally, these species share similar reproductive behavior in that they practice internal fertilization. This fertilization behavior means that male sharks release sperm inside female sharks to fertilize eggs. Only 1 or 2 eggs are fertilized at a time, which contributes to slow population growth and recovery.

The difference in shark reproductive behavior is that some sharks give birth to live babies. These sharks are known as viviparous. Other sharks, however, lay eggs and are known as oviparous. This article takes a closer look at egg-laying shark species.

Egg-Laying Sharks

Researchers report that around 40% of all sharks in the world are oviparous, or egg-laying. Shark eggs are protected by a special case, also known as a mermaid’s purse, when they are laid. Sometimes these egg cases have long strands hanging from them, which serve as an anchor and allow the egg case to attach to seaweed and coral at the bottom of the ocean floor. In other cases, shark egg cases sink to the bottom of the ocean, where they rest under rocks or other ocean floor debris. The mermaid’s purse is often slightly transparent, which allows the development of the embryo to be observed.

Bullhead sharks are another egg-laying shark species. This type of shark is divided into 9 distinct species, all of which belong to the Heterodontidae fish family. All bullhead shark species prefer to inhabit warm, tropical waters and search for food along the bottom of the ocean floor among rocky reef areas. Mollusks, crustaceans, and sea urchins make up the majority of its diet. The largest of these species can reach lengths of up to 5.5 feet, while the smallest of these species reach only 2 feet in length. The bullhead shark is considered a relatively small shark species. Bullhead sharks are recognized for their swimming style, which is generally described as a back-and-forth type of wiggling. The female bullhead shark lays slightly pointed, oval-shaped eggs, which she pushes down between cracks in rocks at the bottom of the ocean. This behavior serves to protect the embryo, allowing for its full development.