Pro tip: This guy is not very nice, according to the encounter Nemo had with it, it did not end very well. If you encounter one just swim away and observe from a safe distance. When killed they drop angler gel which have their certain uses, its best to fight these with at least a Megalodon.
Anglers are found in the deeper parts of the ocean, finding them is as one would guess easy as their lures are easy to see at a distance, they are comparatively easy to kill for gel ( taming food for Mantas and the best fuel in game ) but in groups exceeding three then I suggest running, best take a megaladon.
Also can be lured by other tamed anglers lures.