Building a trap is completely unnecessary for taming sharks as they are very slow. Just use a fast mount that allows you to shoot from the saddle - preferably a sarco or bary, but an ichthy will do just fine as well.

Shoot it until with tranqs til it gets close, then swim a little ways away to reposition, and rinse/repeat. I'd recommend going back-and-forth or in a circularish pattern so you minimize the number of other threats that will get involved.

When it's KO'd, other ocean critters will leave it alone. The only thing to worry about at that point is other animals attacking it when it finishes taming, so it's a good idea to come back just before it finishes and draw the aggro of any other sharks etc that spawned while you were waiting so they attack you instead of your new friend.