More on Sharks

Sharks, the Cannibals

Sharks reproduce in a variety of ways. When it comes to live-bearing sharks, for example, it’s gets even weirder. Take the False Catshark for one. Called Pseudotraikis microdon by it’s beloved fans (erm, scientists), this viviparous, deep sea predator exhibits two very odd and very specific forms of reproductive activity: oophagy and uterine cannibalism.

As you know now, viviparity is a method of live-bearing reproduction that can be divided into three detailed categories among sharks: yolk-sac viviparity, histotrophy and oophagy. The most common form of condrichthyian reproduction, yolk-sac viviparity means a shark carries her fertilized eggs until they are grown pups (baby sharks) ready to be born and swim away on their own, usually when the nutrition from their yolk sacs has been depleted. This is called a lecithotrophic process, meaning the mother does not provide any additional nutrition for her young beyond their individual yolk sacs, which are soft, water-balloon like eggs.

Histotrophy and oophagy are little different. In both types, the mothers provide a sort of extra nutrition to aid their growth of her pups, which is referred to as a matrotrophic mode of reproduction. For example, histotrophic pregnancies provide supplemental milk or histotroph to replenish yolk sacs.

Here’s the interesting stuff: oophagy. In this matotrophic mode, sharks continue to ovulate while pregnant, and these eggs are absorbed by the fertilized, growing sharks to replenish their yolk sac supply. Imagine the pup sharks to be like pacman, gulping down extra eggs as they appear. Popular sharks that give birth like this are Thresher sharks, Shortfin Makos and Porbeagle sharks, for a few.

Some sharks take even further, feeding on sibling pups in the uterus growing along with them. Called uterine- or intrauterine cannibalism, it has been observed in specimens of several larger sharks including Longfin Makos, Sandtiger sharks and more recently False Catsharks. These sharks are also oophagous, so they absorb unfertilized eggs and eat their siblings to survive and get big enough not to be the usual prey.

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