Gutshot--That poisoning was one of many "experiments" in the 1950s which were abject failures. The Park Service wasn't alone in its folly, however. The N. C. Wildlife Resources Commission took a similar approach on Big Santeetlah and it has never been the same.
As for the Park, the list of missteps is long. I note many of them connected with fishing in my book on the Park, and there's a world of insight in Margaret Brown's fine book on the history of the Park.