Inter-annual and diel patterns of the drift of cyprinid fishes in a small tributary of the Meuse River, Belgium
2006
Sonny, D.(University of Liege, Tihange (Belgium). Lab. of Fish Demography and Hydroecology) E-mail:[email protected] | Jorry, S.(University of Liege, Tihange (Belgium). Lab. of Fish Demography and Hydroecology) | Wattiez, X.(University of Liege, Tihange (Belgium). Lab. of Fish Demography and Hydroecology) | Philippart, J.C.(University of Liege, Tihange (Belgium). Lab. of Fish Demography and Hydroecology)
The present study examined fish drift, water temperature and light intensity in the River Mehaigne (Belgium) over a two-year period using a two-fold method that combines punctual 24 h samples with 3 weekly 1 h dusk samples over the drift season. Inter-annual comparisons revealed variations in the relative abundance of Rutilus rutilus and Leuciscus cephalus, explained by a reduced spawning success of chub due to a lower mean water temperature in 2004. Cyprinid larval drift peaked under increasing temperatures, whereas river discharge and turbidity had no apparent effect. A nocturnal repartition of the diel drift distribution was observed, with the highest drift density during late dusk suggesting a loss of rheotaxis in dark conditions. Moreover, the mean body size of roach and chub varied significantly between different times of the day, roach body length increasing from dusk to dawn, whereas chub length was smallest at night.
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