Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8569
Title: Small larvae in large rivers:  observations on downstream movement of European grayling Thymallus thymallus during early life stages
Author: C. van Leeuwen, T. Tokk, Thrond O. Haugen, Peter M. Kiffney, J. Museth
Publication Year: 2017
Journal: Journal of Fish Biology
Volume: Early view
Keywords: larval drift, large river systems, early life stages, spawning, salmonids, grayling,

Behaviour of early life stages of the salmonid European grayling Thymallus thymallus was investigated by assessing (i) the timing of larval downstream movement from spawning areas, (ii) the depth at which larvae moved, and (iii) the distribution of juvenile fish during summer in two large connected river systems in Norway.  Trapping of larvae moving downstream and electrofishing surveys revealed that European grayling larvae emerging from the spawning gravel moved downstream predominantly during night, despite light levels sufficient for orientation in the high-latitude study area.  Larvae moved in the water mostly at the bottom layer close to the substrate, while drifting debris was caught in all layers of the water column.  Few young-of-the-year still resided in the study area in autumn, suggesting large-scale downstream movement.  Together, these observations advocate that there may be a deliberate, active component to downstream movement of European grayling during early life stages.  This research signifies the importance of longitudinal connectivity for European grayling in Nordic large river systems.  Human alterations of flow regimes and the construction of reservoirs for hydropower may not only affect the movement of adult fish, but may already interfere with active movement behaviour of fish during early life stages.

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Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.
Characterize the interaction of human use and habitat distribution, quantity and quality.