They spawn a lot in the Ice Cave on the Island. Since they’re in a cave they respawn fast too. My tribe leader made it out of there with multiple stacks of angler gel. It was actually starting to encumber him.
It seems there is a strange circular underwater hill near herbivore island that is apsolutely crawling with anglers, how many does that mran? Well I've seen about the entire rest of the ocean's population of anglers all at that hill
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.
For some reason, they aggro Kairukus (Penguins) when in the wild. Aberrant versions can and will attack you in surface waters as well, learned that they aggro Kairukus by summoning an Aberrant Angler and then a Kairuku in front of it then it aggroed it! (The Kairuku was wild)