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