Why would an atheist want to deny this? If it's true and you want to think that it's somehow also applicable to humans, it makes the story of Jesus even less remarkable because it provides a scientific explanation for something that was supposed to be magical.
Or were you wanting to argue that this shark's virgin birth is also magical, and that this baby shark is a messiah of sharks?
The first reply he got in the original thread was off me and it was along these lines. He just ignored it as far as I'm aware.