First of all, I usually find them near a body of land. I found one in south zone 2 or south zone 3. And please only tame them the same food, I was taming one with raw fish meat, but ran out of it so I fed with cooked meat, and lost all taming progress. It's filled with mantas outside but I was lucky to only have 1 manta surrounding it, and use itchy to avoid mantas since riding aquatic animal will make you avoid dangerous creatures, even meg's which I tested.

Oh and another thing, there is this creature on The Island where when you click, it gives you tons of prime fish meat, I used it when I was taming with fish meat but then lost some taming progress. So definitely find one of those things where it gives you raw prime fish every 10 mins, it gives you 40+ btw