I imagine there are plenty of large mouth in SD once you ask around with the locals. As you probably know, the size of them directly correlates to the latitude. I live in central Minnesota and was a die-hard large mouth fisherman back 25 years ago. I've got a 6 lb. 9 oz. on the wall which was considered "bass of a lifetime" for this latitude, at least back then. So..... you're not gonna catch any big hogs up here but I probably boated over a thousand decent fish over the coarse of four or five years. At that time our state record was 8 lb. 12.75 oz. for perspective. You can catch 2-4 ponders up here all day long, especially in the first hot weather in June in 2-4 ft. of water in reeds or pads. Fun stuff!