European grayling. Photo courtesy of Rod Calbrade.The European grayling (Thymallus thymallus) is a member of the salmon family (Salmonidae) and can be found throughout the UK and mainland Europe. Unlike Atlantic salmon and sea trout, European grayling are generally potadromous, which means they migrate only within freshwater. Migration is usually driven by a change in habitat requirements as the fish grow, or to find suitable spawning habitat.
A life history confined to the freshwater environment renders this species vulnerable to changing river conditions, and some populations have suffered declines in recent years. The GWCT has been involved in the Wylye Grayling and Trout Survey since 2007, which monitors grayling and brown trout populations in the River Wylye, Wiltshire. It is one of the most comprehensive surveys of grayling population abundance in Europe.