Abiotic control of brown trout (Salmo trutta L.) population dynamics by highly variable stream flow regimes in a central Iberian mountain basin

The main objective of this study is to find out effects of natural variability of stream flow regimes on the principal parameters of a brown trout (Salmo trutta L.) population. Following the work hypothesis from which highly variable hydrological conditions can lead to a clearer response of the population, works were conducted in a high mountain basin in Central Iberian Peninsula, characterized by a continental climate and variable natural flow regimes. Both population dynamics parameters and hydrological regimes were estimated annually in fourteen sampling stations spread in the whole basin during a period of five years, between 1998 and 2002. Correlations between hydrological and population variables were analysed and statistical significance tests were conducted. Four strong linear relationships were detected: two of them describing a link between young-of-the-year recruitment and flow variables; and other two relating mean fork length of age classes 0+ and 1+ to hydrological variables. Meaning of the observed relations is discussed and implications for river related resources management, as well as for further research, are proposed.