No I don't think so, I catch heaps of them whenever I get caught in a storm, sometimes even 2 in a single night if I'm quick with the harpoon but they do spawn a fair bit.

Sounds like you are looking for them at the right times, but not having any luck. Just keep sailing around til you find them, and make sure when you look at your map, it is ''Ocean'' biome, otherwise they won't spawn in shallow water.