From Bulbapedia, the community-driven Pokémon encyclopedia.
A Pokémon watcher (Japanese: ポケモンウォッチャー Pokémon watcher) is a Pokémon Trainer who prefers studying Pokémon in their natural habitats rather than battling them. Pokémon watchers travel the world, and go looking for all kinds of Pokémon so they can observe and study their characteristics and abilities. They also search for new, undiscovered Pokémon.
They often write reports to be reviewed by Pokémon Professors.
Pokémon watchers, like some Pokémon researchers, are known to be eccentric due to their overwhelming fascination with Pokémon. The famous Pokémon watcher Dr. Quincy T. Quackenpoker, for instance, devoted his entire life to studying Magikarp.