From Bulbapedia, the community-driven Pokémon encyclopedia.
Wailmer Island (Japanese: ホエルコ島 Hoeruko Island) is an anime-exclusive island located somewhere off the coast of Hoenn, between Slateport City and Ever Grande City. It appeared in Island Time.
Surrounded by dangerous whirlpools, it does not officially appear on any maps. The island's only known inhabitant, Robin, gave it its name after his friend, a Wailmer that saved him after he fell overboard from a ship a long time ago. Wailmer Island features a rocky coast dotted with sea caves as well as fruit- and root vegetable-filled forests.
Team Rocket had lured Ash and his friends onto their aircraft in a ploy to steal Pikachu. However, after their airplane ran out of fuel, James and Meowth were forced to land on Wailmer Island. They, along with Ash, his friends, and their Pokémon, subsequently converted the crashed aircraft into a ship that would help themselves and Robin escape from the island. Team Rocket then attempted to steal Pikachu and the makeshift boat, hoping to leave Ash and his friends stranded. However, Wailmer Island's whirlpools destroyed the vessel, and they were sent blasting off by Wailmer, who later evolved.
Afterwards, Wailord helped Robin and the group escape Wailmer Island, and they soon located a ship. While Ash and his friends decided to continue on their journey, Robin returned to Wailmer Island to enjoy the freedoms and self-sustainable lifestyle offered by the island.
Pokémon seen on Wailmer Island