The problem is that we are trying to attach a single type of attack to all species of shark.
Some sharks bite, hang on and shake, and keep on biting.
Some bite, retract their jaws, and keep biting, almost burrowing in.
Some bite, then stay close, waiting for the prey to falter.
Some grab a bite, then swim on, satisfied with their mouthful of whale.
And some just swim along, mouths open and thinking 'Mmmm, krill... my favorite.'
I very much doubt that any of my players would be at all surprised if some of my sharks had Grab, and others did not.
The Auld Grump