IMHO >4" BG are not very vulnerable to <16" LMB. I base this on findings of numerous DOW where prey are sampled and then the data normalized to relative predator length. These data indicate that LMB rarely take prey larger than 1/4 their length. After digitizing the curves of the frequency distribution, I found the curves to fit a log normal distribution where 95% of the samples were less than 25% of the length of the LMB.
The mode of the data was ~ 18% the length of the LMB. IMHO this mode, the peak of sample frequency, represents the most energy efficient prey size for LMB taking into account both vulnerability of prey and energy content. Though larger prey have more energy content, there is probably a declining benefit owing to the greater difficulty of capture. Given the condition of your largest LMB, I do think >4" BG would be very resistant to predation after an acclimation period of 24 to 48 hours. I can tell you that the study to which I refer is changing how at least some DOWs are stocking advanced fingerlings in impoundments with existing fish populations. These findings are giving them the confidence to stock fingerlings of shorter lengths than they previously thought would be successful. This is having the effect of decreasing costs, increasing numerical yields, and increasing fishing opportunity in the those states.
What would be missing in your pond is the presence of the YOY that would be optimal for the LMB that might be large enough to successfully predate the stocking. Even so, these LMB have low RW and they may avoid the risk of expending too much energy chasing prey that are difficult to catch. Furthermore, if BG are not currently present in your pond, these older LMB may lack the learning necessary to capture BG of this size with efficient costs of effort and energy. If you are concerned, you could cage the BG to grow out to a larger size. Another option is to feed them behind a blocking net where they would produce YOY while you grow them out. Under the option of a blocking net, wading birds may be the greater predator and some protection from them may be in order. All in all, I think you would lose a few BG either way but that the stocking rate is a good one that will allow the establishment of a population of BG and that will produce copious quantities of YOY prey for your existing population of LMB. Were it me, I do what you were advised but may use a seine as blocking neck to acclimate the BG for 24 to 48 hours before releasing them to swim freely in the pond.
