Comments on: In-utero Cannabalistic Fratricide?

Question: In-utero Cannabalistic Fratricide?

inging — Tue, 21 Jun 2005 13:45:59 -0800

Help me prove I'm not crazy. I swear I saw a documentary about sharks, at one point in my past, and I swear this documentary mentioned that some species of sharks have single births due to the fact that though they are fish, their eggs hatch while still in the mother's 'womb'. Then it's every baby shark for itself, and many times sibling sharks devour one another before being born into the sea. Nobody believes me, and I can't seem to find anything to back up what I think I know.

By: bshort1974

bshort1974 — Tue, 21 Jun 2005 13:55:49 -0800

This article seems to back that up.

By: peep

peep — Tue, 21 Jun 2005 14:00:58 -0800

I saw that, too, and it was a few years ago during Shark Week on the Discovery channel. I think I remember they had footage of this happening, from inside the shark's uterus. I might be crazy, though. And I know this doesn't narrow it down very much, sorry!

By: nylon

nylon — Tue, 21 Jun 2005 14:09:34 -0800

It does happen. Peep is right - they had endoscope footage of a tiny baby shark swimming round in the womb, in a weird soupy/vomity liquid, devouring its siblings. It's all about competition and threat.

It was during the same documentary that a small group of alpha chimpanzees (or gorillas, I can't remember) went on some crazed killing spree, running through a colony and grabbing baby chimps/gorillas and swinging them round their heads. The theme of the programme was obviously 'animals killing other animals'.

By: DelusionsofGrandeur

DelusionsofGrandeur — Tue, 21 Jun 2005 14:14:41 -0800

I saw this tonight on BBC Prime on a program called Weird Nature. The sharks were Tiger Sharks or Sand Sharks or Sand-Tiger Sharks and the segment was filmed off the coast of South Africa. The journalist was bitten by a shark while filming underwater.

BBC Prime website doesn't have much info, only schedules.

By: pwb503

pwb503 — Tue, 21 Jun 2005 14:40:42 -0800

Maybe my girlfriend will chime in here with the authoritative "marine biology grad student" answer, but from what I recall this does happen but not with all sharks.

By: Specklet

Specklet — Tue, 21 Jun 2005 14:44:02 -0800

I have no proof (other than the article bshort has provided), but I have the heard the same thing about tiger sharks.

By: Danf

Danf — Tue, 21 Jun 2005 14:53:49 -0800

Sharks are born live, rather than from laid eggs. . .just deal with it.

By: joaquim

joaquim — Tue, 21 Jun 2005 15:14:08 -0800

Sharks are born live, rather than from laid eggs. . .just deal with it

Do a search on "oviparous" and "shark".

By: ROU_Xenophobe

ROU_Xenophobe — Tue, 21 Jun 2005 16:07:10 -0800

Sharks are born live, rather than from laid eggs

That will come as a shock to the many of us, me included, who've picked up shark egg cases on the beach.

By: salad spork

salad spork — Tue, 21 Jun 2005 17:06:53 -0800

It would have been more accurate to say, "Some sharks are born live, rather from laid eggs." There are oviparous and viviparous varieties of shark.

The in-womb-devouring thing is new to me, but fascinating. In biology, it seems to me, the truth is often stranger than fiction.

By: croutonsupafreak

croutonsupafreak — Tue, 21 Jun 2005 17:24:38 -0800

Considering the size and weight of the newborn, it appears that feeding on eggs or siblings is more effective than depending on the highly specialized yolk placenta.

bshort's link is awesome!

By: madman

madman — Tue, 21 Jun 2005 21:35:26 -0800

Yes, I like watching documentaries on sharks, and this is the tiger shark you're talking about. I saw it too, and always tell people about this whenever they talk about how miraculous "nature" is. :)

By: ikkyu2

ikkyu2 — Tue, 21 Jun 2005 21:54:59 -0800

I dissected a shark in bio lab, and I can attest that there were baby sharks of varying sizes free in the body cavity. I did not dissect the babies to see if they contained even smaller sharks in their stomachs.

By: tomble

tomble — Wed, 22 Jun 2005 01:39:30 -0800

Weird! I heard about this on the news last week. Australian scientists were looking at ways of producing more of this type of shark.. AH HAH!

Grey nurse sharks!

All the evidence you need.

By: borkencode

borkencode — Wed, 22 Jun 2005 03:43:08 -0800

I recall seeing something about this on the Animal Planet channel, and the world's most extreme animals. They had the inside-o-scope with the gross soup. I'm fairly sure that the shark was the Thresher Shark, this seems to back me up, but I'm not 100% certain.

By: cgs06

cgs06 — Wed, 22 Jun 2005 06:10:46 -0800

The term you're looking for is ovoviviparous.

By: agregoli

agregoli — Wed, 22 Jun 2005 09:33:54 -0800

Sevengill sharks also birth live pups.

By: pwb503

pwb503 — Sat, 25 Jun 2005 23:44:54 -0800

I'm pwb503's girlfriend and I used to teach a shark bio class and so have a little background in the subject matter.

There are three main types of shark development:
1. Oviparous: eggs are laid and juveniles hatch like most other fish. Examples: rays, skates (which are in the same class Chondrichthyes as sharks and other cartilaginous fish like ratfish) and lemon sharks. Those are most likely the egg cases you find on the beach ROU_Xenophobe. [If intact, you can frequently hold them up to a bright light and still see the young moving around inside.]
2. Viviparous: live birth, young feeds from placenta. Examples: Porbeagle, whale and blue.
3. Ovoviviparous: eggs form and then hatch within the mother. Examples: nurse, thresher.

The third case is when in-utero cannibalism can happen. In fact, most sharks have two uteri (and males have two genital organs called claspers), so the fight for dominance is happening in each uterus and then usually two juvenile sharks are born.

Sometimes the literature refers to all development that results in live young as "viviparous" even if that development is due to eggs hatching within the female, so it gets confusing.