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Five Wild Facts About Shark Reproduction

August 04, 2021

How much do you know about shark reproduction? We think some of these facts might surprise you!

Dogfish embryo actively swimming inside egg case. Dogfish embryo actively swimming inside egg case. Credit: NOAA/Okeanos Explorer.

In our ongoing effort to help you #KnowSharksBetter, we wanted to share some lesser-known facts about how sharks make more sharks! 

Egg case with dogfish embryo
Egg case with dogfish embryo inside. Credit: iStock

Who Runs the World?

Some female sharks are so self-sufficient they don't even need a male shark to have babies! Females from at least two different species of sharks that were separated from males have had pups without mating. Genetic testing showed that the baby sharks, also known as pups, only carried the female’s DNA. This indicates they had been conceived by asexual reproduction.

Reality TV-Ready

When females do mate with a male, sometimes it’s more than one. Female sharks have been known to use the sperm from multiple males when they reproduce—meaning that pups in one litter could be half-siblings.

12 week old porbeagle shark embryo with teeth.
A 12-week-old porbeagle shark embryo already has teeth! Credit: Sulikowski Lab

It's a Pup-Eat-Pup World

Sharks will eliminate all competition--even in the family. The largest embryo in a shark litter sometimes eats its brothers and sisters in the womb! It’s called “intrauterine cannibalism." Researchers studying sand tiger sharks noted there might be 12 in the womb but the biggest will consume the rest. This allow sharks to have 1-2 bigger babies at birth and increases the odds of survival.

104 Weeks Along

Some shark species carry their young in their womb, similar to mammals. The spiny dogfish shark can be pregnant for up to 24 months—making it the longest gestation period of any vertebrate. And you thought 9 months seemed like a long time! 

Catshark eggs gestating in an aquarium.
Catshark eggs gestating in an aquarium. Credit: iStock

135 and Counting

While the number of pups in a litter varies widely depending on the species, some sharks can give birth to huge litters. For example, the blue shark is known to give birth to as many as 135 pups in a single litter. Imagine that daycare tuition!

Last updated by Office of Sustainable Fisheries on May 02, 2022