Pat,
Brush has worked very well for me to concentrate Crappie for fishing. I think as means for increasing recruitment the effect may be less than we imagine.
It's not clear to me why you are not recruiting. There are lots of choke points that could be affecting BCP recruitment. The first is bedding and swim up. If BCP nests are overcome with predation of eggs and hatch fry, then a bottom up approach may fail to get recruitment of free swimmers in sufficient quantity to recruit in desired numbers. It will take a couple of years to grow to invulnerable lengths. If there are not enough of them reaching 2" lengths to survive all that predation ... poor recruitment will result.
I think your best chance will be supplement stock larger sizes of BCP fingerling. My analysis for 24" LMB, is that the optimum prey size of BCP is 5 5/8" long. At this length, they are very attractive prey for LMB of that length and would be very vulnerable to predation. At longer lengths, BCP are less attractive because LMB will fail more frequently than with the optimum length. IOWs, to consume the same amount of energy, they will have to try more times. With 8" BCP, a 24" LMB will have to make 3 times the predatory attempts as they would 5 5/8" BCP to consume equal amounts of energy. So long as more optimum prey is available, LMB behavior will be to concentrate on the more vulnerable ... more optimum prey. Long story short, 8" BCP stand a pretty good chance of surviving to longer lengths and attaining lengths that your 24" LMB cannot consume.
The most vulnerable period will be just following release of 8" fish. Under normal circumstances, a 24" LMB would ignore healthy 8" BCP as prey. But when released into your pond, they will be naive about predators and they will be stressed and/or possibly disoriented. They will be more vulnerable than if they had grown out in your pond. So there could be, (and probably will be), losses over the first 2 or 3 days as they acclimate to the new environment. There are number of ways you could reduce losses during this period. Things I would consider trying ...
1. Acclimate the supplement stocking as recommended by Ewest behind blocking nets for 24 hours.
2. Supplement stock at cooler temperatures when LMB metabolism is lower. For example, an 8" BCP provides 2.34 days' worth of energy at 62F to a 24" LMB. At 78F, it would only provide 1.3 days of sustenance. Lower temperatures increase the handling time giving the supplement stocking more time to acclimate.
3. Co-stock with cheaper but more optimum prey that will be more attractive for consumption and more vulnerable to predation. For example, 5" - 6" GSH. This sacrificial prey could be additionally stressed to make them more vulnerable than they would otherwise be. Just enough to get your BCP through acclimation.
4. Time for vulnerability of your TP (provided temps are high enough to transport your BCP).
I think a recruitment rate of 30 >8" BCP per acre-year would sustain a healthy adult population. At 30% annual mortality, over 5 years of growout, this recruitment rate (combined with mortality) would maintain an adult population of ~83 BCP per acre and a potential standing weight of 100 lbs/acre.
If I were to try this, I would start by trying to establish that 83 BCP/acre population right from the get go. I would supplement 80 or so 8" BCP/acre. Then the following year I would supplement 30 BCP/acre. By the end of 2nd year, if you were able to successfully recruit, you would have 8" BCP recruits some of which you would need to crop.
It's not clear whether you will be able to recruit, but to give yourself the best chance, you will need to protect the adult population until they reach a minimum length or age. This would ensure a good standing weight of adults to give you your best chance at in situ recruitment. If unable to recruit, 30 BCP per acre-year should maintain a fishable population that you can harvest at some minimum length or age.
