The other purposes would be:
To brain fish
To use as a bar to dislodge an urchin and get it in the bag
To clean the urchin once back on shore
To hold down a pissed off crab while you measure it
To cut a multitude of lines, ropes and entaglements
To bang and pry on stuff that need prying and banging
To fight off enemy divers
To piss off people who don't like big dive knives
And because they look cool.
Here you go:
Rambo Knives for Sale
You can pretty much forget about any criticisms (to your face anyway) with one of these babies! 420 stainless takes a decent edge, just baby it a little to control rust. You could build one from Titanium but you would have to add some mass to be a good scallop bar.
You can't beat a diver's hammer and stainless Abalone bar for scallops. Just tell the game warden that it is an emergency signaling device. The mushroomed end of the ab bar could be a problem though.