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
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)
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.
Since they tend to retreat and charge after taking some damage,having a fast water mount (or at least flippers) is good to get off and back on when trying to ko or kill. I prefer the Sarco for its AoE bite against multiple and infinite stamina in water (however it only has one speed in water anyways, but it's still fairly quick depending on level). If escape is necessary bite it with the Sarco when it gets too close and swim away when the angler retreats. Crossbows (and most, if not every, other weapon) do work on its back, if you'd rather not get off.