The effects of a major flood on an endangered freshwater mussel population

During February 1998, a 100-year return flood occurred in the River Kerry, north-western Scotland. A study was undertaken in order to assess the impac t of this event on a large, internationally important Freshwater pearl muss el (Margauitifera margaritifera L.) population. A conservative estimate of 50,000 mussels killed by the flood was made. This represents 4-8% of the to tal population. Significant channel reformation and large-scale movements o f substrata occurred in some reaches, whereas others appeared to be unchang ed. Some mussel beds disappeared or were largely depleted whereas others re mained intact. Boulder-dominated substrata appear to have provided the most protection from scouring. The relatively high mussel densities and recruit ment levels found in the middle reaches are probably due to the fact that t his part of the river is hydrologically stable. It is likely that the intac t mussel beds in the middle reaches will be the main source of regeneration in other parts of the river as the population recovers. As a result of rec ent changes in the hydrological behaviour of Scottish rivers, several M. ma rgaritifera populations may now be more at risk from these catastrophic eve nts. Therefore, it is important that conservation managers are aware of thi s potential threat. (C) 2001 Elsevier Science Ltd. All rights reserved.