One other piece of info that affects recruitment. Though it is a small pond it has lots of structure. We reclaimed the pond in the late 80s dredging it down to 20' deep and taking tens of thousands of cubic yards of material out and selling it. First it was top soil, then common fill, then a layer of clay, then bank run sand and gravel. We went through some ledge material too and those "boulders" and rock were laid along the 45 degree shoreline slope for structure and to hold up the bank. So basically the entire pond is lined with an underwater stone wall. Plenty of places for fry and juvenile fingerlings to hide plus there is a good crawfish population. With new water coming in from three small brooks and the bank run springs there is plenty of new "food" for supporting zoo plankton and the herring fry during the summer is measured in the tens of thousands so if a fish can keep from being eaten then there is plenty for the fish to eat. Yet the pond fisheries bio-mass never seems to change much. It is much denser than Ball Pond or Candlewood on a cubic yard of water basis but at some point the pond has its limits no matter the circumstances. And I have otters, mink, cormorants, mergansers, other divers, great blue herons, small herons, ospreys, bald eagles, water snakes, king fishers, etc. all eating at the pond's expense. Did I miss any predators?