I would try to rule out predators of the two legged, ten toed, variety. Part of the problem could be there.
Another possibility could be that you have a LMB population in balance with the available foods. It would not be possible to have 100 LMB at 3 lbs each in a 1 1/4 Acre pond earning a sustainable living on in situ produced forage. As fish grow, competition for food creates a mortality headwind where survivors tend to be the fish that ate at the expense of their peers. There will ultimately be balance between the biomass of LMB and the foods that support and grow them. Mortality is the penalty for not competing for a limited source of food and this allows for continued growth of survivors. At your location, around 5.70 lbs of consumed forage is needed to maintain 1 lb of LMB biomass. You mentioned that your catch rates are low. Can you provide specific details on times spent fishing and how many were caught? Also, the sizes of your LMB are important. The larger they are, the fewer of them that you have (and vice versa).
The feed trained 85 averaged 1.5 lbs (just averaging the 1 to 2 lbs at stocking) and that estimates to ~125 lbs just for the feed trained LMB. Was this rate of stocking recommended to you? 125 lbs of LMB in your climate can be supported on yearly consumption of ~368 lbs of high-quality feed. If all survive, they cannot grow on that yearly ration. But if say 25% of them die each year, the survivors will fill the biomass that 368 lb ration will support. IOWs 368 lbs of consumed feed will grow 64 LMB to fill the 125 lbs the feed will carry where they will average 1.95 lbs (growing 33% in weight). So a good question is how much are they fed annually and how much of that feed is being consumed directly by LMB?
Something to keep in mind about feed trained LMB. Winter can be tough time for them. In the six months from October 1st to March 31st, in an average climate year at a DFW location, LMB need around 1 lbs of feed for each pound of body weight. LMB are less active during this period and feed may not be consumed as readily as in summer. When feeding is curtailed during the cool months, feed trained LMB would have to compete with the other LMB for live fish prey. This creates headwinds for both the feed trained LMB and those that are not.
I am not sure what your expectations are in terms of the survival of your stocked LMB but you may have higher expectations than what is possible in a 1.25 acre pond taking into account forage and feed consumption. So it can be difficult to distinguish between what is mortality due to unwanted predators and what is normal mortality given the food consumption limitations. Whatever it is, you will want to pin it down before stocking more fish.
