Grayling population of national importance: distribution area

The data on grayling populations of national im-portance includes four subproducts; the distribution area layer includes the sections of watercourses with 20 major grayling populations of national importance. The core data come from the atlas of fish and cyclostome distribution in Switzerland (Pedroli et al. 1991), cantonal catch statistics and information from the cantonal management of fisheries.