Mother sharks return to Puget Sound to give birth to pups, and then these siblings make a point of sticking together.
..."What we're interested in is if we can flip this observation around: Are the relationships we're seeing between brothers and sisters traveling together and staying together as juveniles transferable to other shark species as well?" said Christiansen. "We don't know; we'd like to see some effort going into other shark species to see if that's present."
And while you're at the Discovery website, click through Michael Reilly's slideshow of the latest bizarre finds from the Census of Marine Life.
(Photo of Blunt-nose Sixgill Shark [Hexanchus griseus] off Seattle by Dan Hershman)