Some species of pokemon are more common than others. For example, Magikarp can be found almost everywhere. They are pretty hardy and produce eggs quickly. But there are also some other species of Pokemon that only live in one particular area or don't produce eggs very fast so that keeps their numbers low.
Wailmer and Wailords aren't as rare, as say, a Lapras, but they aren't very commonly seen either. Which is a good thing, in a way. They require a tremendous amount of food every day. If there were too many in one location, they'd go hungry.
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Some species of pokemon are more common than others. For example, Magikarp can be found almost everywhere. They are pretty hardy and produce eggs quickly. But there are also some other species of Pokemon that only live in one particular area or don't produce eggs very fast so that keeps their numbers low.
Wailmer and Wailords aren't as rare, as say, a Lapras, but they aren't very commonly seen either. Which is a good thing, in a way. They require a tremendous amount of food every day. If there were too many in one location, they'd go hungry.