El estrés térmico e hidrológico impiden la supervivencia de Margaritifera margaritifera L. en ríos de montaña: una constatación empírica

The distribution of Margaritifera margaritifera in four mountain rivers of Castilla & León (Negro, Tera, Águeda y Alberche) has only been known for two decades. They are small relict populations at the southern limit of their global distribution and are singular in the Mediterranean region. The thermal water regime has been studied as a stressor for populations that have not recruited for decades and are composed of senescent adults at theedge of their fertile stage. Increasingly intense and longer droughts reduce the riverbeds extension that can support naiads and trout, with insufficient flow in summer and autumn, which inhibits reproduction. The warming waters limit the survival of all life stages, in the water and sediment as a thermal refuge. Only the epirithron stretches, well shaded by the alder wood maintain, for the moment, sub-optimal habitat conditions. All rivers exceed the critical thermal survival thresholds for juveniles, with the highest rate of increase in the Negro river. The uncertainty of recovery programmes for this species is discussed if it isnot possible to rely on rivers for the reintroduction of captive-bred juveniles due to thermal stress caused every summer by warming and water scarcity.