Random displacement versus habitat choice of fish larvae in rivers

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Abstract
Numerous studies elaborated habitat preferences of early juvenile fish. However, detailed analyses of swimming performance of fish larvae and early juveniles revealed substantial doubts about their ability to maintain positions in the river and to choose habitats. It was hypothesized that the juveniles will be randomly distributed by turbulent flows initially, and that the match with suitable nurseries depends on the shore line heterogeneity. Low swimming performance of juvenile fish, as compared to the flow velocities in rivers, allows consideration of a longitudinal dispersion model as a tool to predict the spatio‐temporal patterns of juvenile fish assemblages, e.g. downstream of a spawning site. Because of variable geometry of the river channel, longitudinal dispersion should be expanded with equations describing the effect of stagnant flow zones which can also act as the refuge. In this study a model of dispersion processes with non‐transit zones was developed and validated for the lowland Müggelspree River, Germany. Computations with the model provide the possibility to explore the effect of flow and channel geometry on the distribution history of juvenile fish. Particularly, the model allows in a probabilistic way to estimate for the portion of juvenile fish retained in non‐transit zones of the flow and subsequently of the portion transported downstream to the lakes, and thus, finally, to assess the importance of random displacement for the spatial structure of the juvenile fish assemblage in a river. Copyright © 2008 John Wiley & Sons, Ltd.

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