National Marine Fisheries Service

08/04/2021 | News release | Distributed by Public on 08/04/2021 09:43

Five Wild Facts About Shark Reproduction

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

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, indicating 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.

A 12 week old porbeagle shark embryo already has teeth!

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, allowing sharks to have 1-2 bigger babies at birth and increasing 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 nine months seemed like a long time!

Catshark eggs gestating in an aquarium.

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 pupsin a single litter. Imagine that daycare tuition!