Is a brook trout really a trout? How come you can keep so many of them?

Technically the brook trout is a char, more closely related to bull trout than to rainbows or cutthroats. They are not a native species in Idaho. The limit is high because brook trout are very prolific and tend to out-compete and interbreed with the other trout species. Brook trout are a significant threat to fishing opportunity for native cutthroat trout and bull trout. They also tend to become stunted when over-crowded in lakes.