There's a similar occurrence on Bull Shoals... decline in shad. But I don't think you can blame that on brown trout can you? Since the lakes are so closely connected, the cause could be the same, could it not?
By the way, MDC doesn't know the reason for the decline (BS), only that it may be a natural progression of an aging, man-made lake... ie. freshwater shrimp/Lake Taneycomo.