Doug,
How deep is the outflow water leaving your pond? In a simple assumption I would think it may be possible to lose forage fish in your outflow. In turn that I would believe would effect your LMB growth. Food chain ect. Crappie in a situation with low forage levels would outcompete your LMB. My suggestion would be to study on the most cost/time effective route to repair your overflow then turn your thoughts to fish. Meanwhile fishing the crappie to try to lower numbers hopefully helping on a possible forage strain. Crappie will rebound if you want them no matter how hard you fish them.
Another simple thought if it is not already in place. Try to install structure on the opposite side of your outflow or in a low current area where your forage fish can hang when the water runs out. That may help save some of the forage fish if they are indeed following or washing away with the current.
