The effects of elevated river discharge on the downstream drift of young-of-the-year cyprinid fishes

Abstract

Increases in current velocity and water turbidity during elevated river discharge can increase the abundance of drifting fish of particular size, age or taxa. We tested the effect of artificial and natural increases in river discharge on the drift of young-of-the-year (YOY) cyprinid fishes in a European river. Elevated discharge affected neither drift abundance nor size, age, or taxonomic composition of drifting fishes. Elevated discharge was observed exclusively during the day and did not alter water transparency, whereas current velocity increased significantly. This allowed us to separate effect of these correlated factors, and we conclude that, at least in structurally complex habitats, water turbidity rather than current velocity is the causative factor for the cessation of diel periodicity in drift and increases in drift abundance during floods. © 2004, Copyright Taylor & Francis Group, LLC.