Ponddragon,
You earlier said the predominant size of GSF that you catch is 4 to 6". What percentage of the GSF biomass is in these sizes? How numerous are the smaller sizes relative to those you predominantly catch?
I can tell you, with little doubt in my mind, that the bulk of the GSF biomass will be comprised of those sizes that cannot be consumed by your LMB. They survive because they have outgrown the majority of LMB (if not all of them). After all, if you had LMB thinning the 4"-6" GSF, wouldn't you see examples of LMB large enough to consume them?
Also, have you given any thought as to why your 7" LMB are so thin? If a 7" LMB is not getting enough to eat to have good condition. How could stocking 6" LMB immediately help? Wouldn't they have just as difficult a time finding enough forage to eat? That is what makes sense. Stocking 6" LMB will fail to help your situation unless you do something about your GSF population, IMHO.
I mean no disrespect to esshup. In his mind, your LMB are underrepresented. And here's the grub, he is right about that. What you need is around 75 or so LMB in small sizes preventing a high population of 4"-6" GSF from developing. This number is a very good recommendation for an initial stocking of LMB where large panfish are a goal. But then, in an initial stocking, the number of reproducing panfish is low. They produce a lot of YOY that can feed those 75 LMB and grow them. You have the opposite situation IMHO. I believe both the population and the Biomass of LMB is underrepresented. I also believe that both the population and biomass of adult GSF are overrepresented. A forage locked pond will not support a good biomass of LMB because prey is in short supply. So what has happened? Your LMB are in balance with the biomass that the forage locked pond can support.
So its more complicated than just a predator stocking. 4CP makes great point about being the predator of GSF. It may be difficult to source LMB that are large enough to consume optimally those 4"-6" GSF. Furthermore, the pond will not support very many LMB that large. Maybe 2 or three max and have acceptable balance (which still would not be ideal). So a population of LMB where the biomass is concentrated in large LMB would not work to grow larger panfish. They will reduce GSF in the 4-6" class, and by doing so, increase the number of GSF smaller than 4" (something counter to goals).
I am going to make a recommendation which is outlined below putting together the best advice you have thus far received.
1. Now is horrible time to stock additional predators. You need to prepare the pond for them. What you want at the time of remedial stocking of LMB is a thinned population of adult GSF producing large numbers of consumable YOY. We are probably looking at the June time frame next year for stocking LMB.
2. You need an adult GSF population that is similar to what would be ideal for an initial stocking with panfish goals. You need to remove all but around 300 of the GSF adult population. If you were to do that, you would have an adult population of 400 GSF per acre.
3. RIGHT NOW, is the time you need to be thinning GSF. Delaying would be contrary to the goal of restoring balance. Thinning now, will allow the remaining GSF to make winter in better condition. This will improve forage production next spring helping the remedial stocking of LMB to grow and control the number of GSF recruited.
4. Mark the first 150 GSF you catch in sizes > 4" and throw them back. Use whatever your preferred method of fishing is to do that. You can use a fin clip to mark them. Throw back marked fish when recaught.
5. After marking, from now until ice cover, remove all the unmarked GSF >4" you can until you are catching a 50/50 mix of marked and unmarked GSF. Use 4CPs method to leverage each cast for multiple GSF caught. If you are still catching more unmarked GSF than marked when the pond ices, then resume this removal of GSF next spring only stopping when there is a 50/50 balance in your catch of marked and unmarked GSF.
6. Watch for your first cohort of GSF YOY. When they reach sizes around 1", do your remedial stocking of LMB. I like 40 to 50 8-10" LMB. If you prefer, go with esshup's rec of 75 6" LMB. But if I were to do that, I would probably stock them before observing the GSF YOY.
I think there is pretty good chance you would see very good result by Fall of next year if you follow these recommendations. With numbers up, the LMB should more effectively control the number of GSF recruiting to the 4-6" sizes, this should be conducive to growing larger panfish. If control is sufficient, you next worry will be over recruitment of LMB. I have fished a lot of ponds with LMB/GSF combination, albeit much further south. All of these ponds had over representation of LMB. But your pond has the opposite condition in this moment.
You may ask why, if the most common condition is over representation of LMB, how did your particular pond develop the opposite condition. The best explanation I can proffer is that there may have been an event that drastically reduced the adult LMB population. The GSF population was not as affected. Once the imbalance was in place more GSF survived to be adults. This condition reduced the production of consumable forage production ... forage locking the pond. So a couple of possibilities. Possible overharvest of LMB, possibly poaching. OR a low DO event that affected the LMB more than the GSF.
