[Crazy Jetty]

Aside from the fact that Jason Abbadon is absolutely right, I'd just like to point out there is a monumental difference between these two sharks mating, and two breeds of dogs.

All dogs (Note, not all Canids, all dogs), are the exact same species. From a weinerdog, to a Great Dane, they are genetically the same. (Housecats, too)
The Austrailian Blacktip, and the Common Blacktip, while closely related, are genetically distinct species.
Discovering a significant wild population of hybrids of these two sharks (And 57 known individuals is a significant population), is akin to discovering a population of elephants that are hybrids of African and Asian. Two totally different, but related species, that have very little interaction with one another, due to habitat. (They used to have mildly overlapping habitats, until man severed it. At least, I believe they did)
While why the "new" sharks are significant has been stated very well, I just felt the need to point out the "dogs" analogy really does not work at all. Completely different thing.