Has there been a determination as to what caused the decline? Most of the streams that they inhabit are pretty stable environments, but something apparently changed. Climate change shouldn't have anything to do with it because they inhabit both streams that have a rather stable temperature (primarily spring fed) as well as streams that vary in temp with the seasons. Some chemical element perhaps? A few of the streams have remote watersheds with little human influence it would seem, while some watersheds have a great deal of human influence.