EFFECTS OF FLOW REGULATION ON BROWN TROUT ABUNDANCE TRENDS IN THE SOUTHERN LIMIT OF ITS NATIVE DISTRIBUTION

The effects of regulated flows on the trends of population abundance is of high interest in order to downscale global change effects on the native range of a given species. This is particularly interesting in the limits of its distribution, being the case of brown trout (Salmo trutta L.) in the Iberian Peninsula. Data series from all over Spain have shown a general negative trend in abundance in the last two decades. Strong correlations were found among abundance trends and naturally driven climate and flow variables. Flow regulation was found to buffer the correlation between brown trout density and time, thus leading to smoother trends in those sites located downstream from large dams with flow regulation capacity. At the same time, dams may reduce the species' resilience that allows metapopulations to recover from naturally driven negative trends due to habitat fragmentation. Long-term and short-term effects of flow regulation on brown trout abundance trends might therefore be antagonistic.