Hidden Killers

Sandtiger shark embryo.jpg
Image source: Virgin Media

Sandtiger shark (Carcharias taurus) pups emerge from the womb as experienced killers. Since they develop teeth and the ability to swim while still in the womb, the strongest embryo will actually kill and eat its siblings (embryophagy) and their yolk sacs. This ensures that the surviving embryo has sole access to the unfertilized eggs that are continuously produced by the mother. Since they have two uteri, these sharks give birth to two live offspring whereas other shark species with less intrauterine killing instincts may deliver a brood of up to a dozen or so. In fact, the sandtiger shark has the lowest reproduction rate among sharks which helps to explain their status as threatened.

Other species of sharks do not have such dramatic sibling rivalries. Instead, they feed on the constant supply of unfertilized eggs produced by the mother (oophagy). This is by far the most common type of intrauterine cannibalism in sharks.

Here is a video of intrauterine Sandtiger shark cannibalism

Sources:
http://www.elasmo-research.org/education/topics/lh_intrauterine_cannibalism.htm

http://animals.nationalgeographic.com/animals/fish/sandtiger-shark.html

http://deepseanews.com/2011/09/shark-siblingicide/

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Wow, this is horribly fascinating!

Is there a problem with the video linking, or is it me? Everytime I click on play for the video, it just reloads the page?

This is a very fascinating blog. I had no idea that other species could exhibit cannibalism, let alone in the womb. However, the video does not seem real. The sharks just look very, for lack of better terms, animated. One question I have after watching the video is how did people get a video of sharks inside a womb, and how did they know that something was going to happen? What was the purpose of videoing baby sharks in the womb?

You are correct Kendall, the first portion of the video is animated. The last portion of the video (~1:58) shows actual footage of a shark embryo feasting on eggs as well as the corpses of its siblings.