In Clark Lake, young-of-year threadfin shad did not reduce zooplankton populations, but in Stonelick Lake, peak abundance of young-of-year threadfin shad was followed by a precipitous decline in zooplankton. Data on cladoceran birth rates indicated this decline was due to increased predation by threadfin shad. Survival of bluegills to a size at which they move into the littoral zone also declined in Stonelick Lake, perhaps because of the virtual elimination of zooplankton. Limited survival of bluegills in turn contributed to reduced growth of young-of-year largemouth bass dependent on them as prey. Given that zooplankton declined in one but not the other lake, interactions among young-of-year fishes due to annually introduced threadfin shad will likely vary among systems and years. Nonetheless, introduced threadfin shad could, in some systems in some years, negatively affect growth and recruitment of the very species they were meant to enhance.
This very clearly states that in one of the two lakes studied, threadfin had an even more negative impact on the bluegills' food source than gizzard shad. And, as I added in my last post, competition for food is not the sole reason shad of either variety, in addition to GSH, will invariably cause a decline in the average size of a bluegill population; the more fusiform prey cause the bass to prey less on bluegill, allowing them to overpopulate their food source. But beyond that, I base my conclusion first and foremost not on the studies, which I referenced just for substantiation, but rather personal observation of fishing many lakes and ponds that had once had large bluegill but since the addition of a fusiform prey no longer do.
