Spatiotemporal Dynamics of Brown Trout Production in a Cantabrian Stream: Effects of Density and Habitat Quality

Abstract

Spatiotemporal patterns of growth, survival, biomass, and production were investigated in seven cohorts of a resident population of brown trout Salmo trutta in Rio Chabatchos, northwestern Spain. Seasonal growth matched the sinusoidal pattern that typifies fish growth in temperate climates. However, all of the population traits examined differed among sites, markedly at one site. Cohort (40.3 g/m(2)) and annual production (41.0 g/m(2)) were greater than reported for other stream salmonids but varied dramatically across sites and years. Stream discharge in March appeared to be the major determinant of annual recruitment, whereas site characteristics related to stream channel structure constrained recruitment at the site scale. Cohort survival showed two-phase trajectories characterized by a long period with low or no mortality followed by increased mortality after a certain point. The point of inflection differed by more than 150 d among sites but occurred at similar trout sizes (15 cm). Recruitment explained 86% of the spatiotemporal variation in cohort size, which, in turn, explained more than 91% of the variation in cohort production. Discharge-dependent recruitment means that recruitment, cohort size, and production are temporally unstable.