This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Plenty of species have been observed eating their own young. Still other species see their young competing for resources, so only the strongest survive. But the grey nurse shark (Carcharias taurus) takes it a step further: its young have a tendency to eat each other, in utero.
You read that right.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
As grisly as it may seem, this reproductive system worked just fine for the grey nurse for millions of years. Until, that is, the rise of modern fishing techniques.
Now, grey nurse sharks are dying faster than they can breed, the victims of drift nets and other commercial by-catch. In Australia, scientists estimate there are just 500 to 1,000 grey nurse sharks left, down from several thousand in the 1980s.
But Nick Otway of the New South Wales Department of Primary Industries has an idea to boost that population. For the last three years, he's researched building an artificial womb that would keep grey nurse pups from eating each other.
Here's how it works in nature: A pregnant grey nurse shark can carry up to 40 embryos in each of its two wombs. When they get large enough, they turn on each other, eating their womb-mates until only one pup is left in each uterus. Under normal conditions, this would create a stable shark population that rarely shrinks or grows.
Otway proposes removing the young before they get to the cannibalistic stage and raising them in artificial uteruses, described as "tubes within tanks." There, they would receive a steady food supply, so they would not need to eat each other, and they would be released nine to 12 months later. Otway told the Sydney Morning Herald in 2006 that "If we can raise about 40 pups a year it will start bringing up the grey nurse population."
It's not an easy process. Otway told the Australian Broadcasting Company that the artificial wombs would need to mimic the environment inside the mother sharks, such as composition of fluids, bacteria, food composition, and temperature, as well as how these factors change through the course of the pregnancy. The scientists also need to master surgical techniques to remove the embryos from the mother and place them into the sterile artificial uteruses.
Will the idea work? Otway and his team successfully tested it last year on dwarf wobbegong sharks (Orectolobus ornatus), a non-endangered species that also raises live pups in its womb. (Although the wobbegong pups tend to eat each other after birth.) Otway has said it could still be years before this technique is perfected, or even tested on a grey nurse.
And there's always immaculate shark conception.
Image: Wikipedia
