My experience with freshwater drum/gaspergou/sheepshead or whatever you want to call them is not exactly the situation you are asking about, but I can tell you what I know. This past summer I collected them electrofishing in several shallow oxbow lakes in Mississippi. Several of the lakes were in the 10 to 30 acre range with maximum depths of 2 to 3 feet and nearly all of them had drum. One 20 acre lake has not connected to the river since 1972, had a maximum depth of a little less than 2 feet and was experiencing frequent low oxygen conditions, but still contained drum.
I can't say for sure that the drum were reproducing, but since the river hasn't connected to the lake in so long the only way drum would still be in the lake is if they were reproducing or people were stocking them in there. Stocking seems doubtful especially when considering the fact that we found a wide range of sizes of drum, which would require multiple stockings.
I am far from being an expert on freshwater drum, but I hope this helps.
