When shark embryos get hungry an unborn sibling makes a tasty treat

Written by: Captain Skellett // November 25th, 2009 // Sex and Reproduction, The Realm of Bizzare

Next time you run out of food in the fridge ask yourself this, would you eat a human? If you were in a plane crash in the middle of a desert, would you eat the person who sat next to you, or would you brave the supply of frozen muffins and green omelettes they serve as sky “food”? For your own survival, would you kill and eat your brother or sister?

Some species of shark do indeed feast on their siblings, not just out in the deep blue sea, but while still inside the uterus. Now that’s taking sibling rivalry to a whole new level.

Sharks reproduce in three ways – they either species lay eggs and leave them to hatch, or they lay eggs and let them hatch in the uterus and then give birth to them, or they have a live births. Feeding a growing embryo while it develops in the womb is quite a challenge for sharks, but they have some crazy methods to do it.

Some species, such as the lemon shark, turn their yolk sac into a placenta by attaching it to the wall of the uterus. Salmon shark embryos eat a stream of unfertilized eggs while their in the womb, providing them with plenty of nummy nutrients. Nurse sharks and sand tiger sharks, at the tender age of not even born yet, swim about and eat their siblings. From the 20 or so pups that start life, only two remain – natural selection starting early *they grow up so fast*

This video from the documentary Animals in the Womb has incredible footage of sand tiger shark embryonic cannibalism.

Why do two pups survive, and not just one? Sharks have two wombs, at least, their uterus has two separate branches that keeps the two pups apart. Apparently having their own room helps curb their aggression, who’d have thought?

Captain Skellett

I be Captain Skellett. Me blog started in April 2009 when I was working full time and didn’t get a chance to talk science. Now I have changed jobs and talk science all the time, but that doesn’t stop me blogging. More About Captain Skellett   Google


4 Responses to “When shark embryos get hungry an unborn sibling makes a tasty treat”

  1. Lab Rat says:

    “Not the Nine O’clock News” had a great sketch like that, a spoof interview with two ‘plane crash survivor’ victims, talking about how they got so desperate for food that they eventually had to do the unthinkable…eat the aeroplane meals. It ended with the wonderful something-along-the-lines-of line “oh yes, well, we’d eaten the other passengers several days ago”

    That’s fascinating about the sharks…I suppose it’s a good way of ensuring that the strongest ones survive, and are well fed too!

    Captain Skellett Reply:

    OMG I can’t believe you know that! That was EXACTLY what I was thinking when I wrote that line! Man I love that show! Rowan Atkinson looks so young – and do you remember the one about John McEnroe? His parents tell him off for slurping his juice and he goes nuts with the “I did NOT make a slurping sound! You are the pits of the earth! You are so INCOMPETANT!”

  2. Lab Rat says:

    Yeah, the John McEnroe one is funny XD I think my favourite sketch has got to be Gerald the Gorrila though, that always cracks me up 🙂 (“David Attenborough, all I ever hear is David bloody Attenborough”).

    Aren’t you based in Australia? I’m surprised “Not the Nine O’clock News” made it all the way out there, it was mostly jokes about Thatcher if I remember.

    Captain Skellett Reply:

    Oh yeah, that one is good too. The refined gorrila – how about the belgian habits one, where Atkinson says if one vomits at the table it is a sign that they have enjoyed the food so much “they wish to bring it back so they can eat it all over again.” Ha! Gross… Love his accent though.

    I found it on dvd 🙂 My mum’s english, so she loves all those shows (Vicar of Dibley, the Good Life…) The Thatcher jokes are a bit beyond me though.

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