I was on the Shreve Branch today, deep in the pines by the Shoal Branch. The Shreve Branch here is only 4 feet wide, and full of logs. I saw a shell and lifted it out. It was quite large, and a recent death. Then, a little way up, a live one, also large. So odd, they must have grown up here, and now are too big for the stream and unable to obtain sustenance (my guess). They seemed about 30 pounds plus by my reckoning.