Population dynamics of brown trout (Salmo trutta) in a breton stream (France) : The non-migrant spawners. The biological factors of the population dynamic of brown trout in a tributary of the Scorff river, have been studied during 4 years . The characteristics of the spawners, present in the stream before the spawning migration from the main river, are described . These spawners were born in the stream and stayed there during their entire life-span . Among mature fish the sex ratio was always in favour of males . During the third and the fourth years of life, annual mortality rate was 70% for males and 50% for females . 1+ spawners were these which had the best 0+ growth rate. A majority of males first matured at 1 + years of age . On an average, 1 + females were responsible for 25 016 of the total reproductive potential . The number of 3 + and 4+ females seemed to depend on the fishing effort .