Who are the stingrays enemys?

The most dangerous predator of sharks are...

...larger sharks!

The shark may also be a prey of killer whales, giant squids and even giant octopus.

Recently it was confirmed, through a night video recording, that the missing small sharks in a big tank of an US aquarium were beeing eaten, during the night, by an octopus that was in the same tank.

Q.E.D.

Post script:

I forget to mention the most obvious enemy of sharks: Homo sapiens sapiens.