From Bulbapedia, the community-driven Pokémon encyclopedia.
Scalchop Island (Japanese: ホタチ島 Hotachi Island) is the second island Ash, Iris and Cilan visited during their travels through the Decolore Islands. It is inhabited by Oshawott and Dewott. The inhabitants sell many goods based on scalchops, the shell weapons used by Oshawott and Dewott. Even the island itself is shaped like a scalchop.
The island hosts a traditional competition called the Scalchop King Competition, concerning Oshawott and its evolved form. On the island, Ash's Oshawott fell in love with a female Oshawott, nicknamed Osharina, who was the winner of the females division of the competition. In order to get her attention, Ash's Oshawott entered the tournament, gaining a rivalry with a Dewott named Caesar, owned by another Trainer. Ash and Oshawott eventually won from them in the final, but were disqualified when Oshawott's scalchop broke because he was heartbroken when he saw Osharina preferred Caesar over him. After that, Ash and his friends left the island.
Pokémon seen on Scalchop Island