Can you keep a smallmouth bass in Montana?

No minimum size, fifteen a day — three times the largemouth bag in the same district.

FWP source page

The opposite of every other bag limit on this page: not a cap on how many you may keep, but a requirement to keep and report every single one caught, because smallmouth bass are not supposed to be in this stretch of the Yellowstone at all.

FWP source page

What we left out on purpose

• Bighorn Lake (a separate water from the Bighorn River this site tracks) carries its own sauger/walleye numbers (6 combined daily, only 3 may be sauger) — not modelled here since this site follows the river, not the lake.
• Gallatin River carries a boat-fishing closure between the Yellowstone National Park boundary and the East Gallatin River, and a fixed general season (third Saturday in May – November 30) on the stretch from Porcupine Creek Road to the West Fork — gear/access rules rather than size or bag numbers, not modelled in this schema.
• The Madison River's Lyons-Bridge-to-Ennis-Bridge stretch is actually two adjoining catch-and-release segments (Lyons–Varney and Varney–Ennis) with a near-identical but not byte-for-byte identical rule (one restricts all trout, the other only rainbow). This site's tracked coordinate sits almost exactly at Varney Bridge, the boundary between them — both are described together rather than forcing a guess about which side of the bridge the coordinate falls on.
• Channel catfish, shovelnose sturgeon, tiger muskie and walleye/sauger are not modelled for these six waters because none of the six carries its own number for them and none is a species this site's water reports actually target.
• Montana's hundreds of further named-water exceptions beyond the six waters this site tracks are not modelled — the same restraint used for Colorado's, Kansas's, Michigan's and Minnesota's named-water exceptions.