The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

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Abstract
SUMMARY: (1) Seasonal variation in the intensity of feeding activity was demonstrated in two chub populations. Feeding activity was higher in summer and more pronounced in the young age‐classes. The intensity of feeding activity was significantly correlated with temperature.(2) The diet of the total chub populations embraced a wide range of food items but vegetable material predominated. Substrate material was frequently encountered which suggested considerable feeding on the river bed. Fish were the most important animal food, by volume, in the River Lugg but Trichoptera larvae were most important in the Afon Llynfi. No remains of salmon parr or trout were found in chub stomachs but grayling were eaten. The most important prey fish, by volume, was the eel but cyprinids, especially minnows, were most important by frequency of occurrence.(3) Seasonal variation in the composition of the diet could be related to availability of food organisms but some selection was shown. Vegetable foods were most important in summer; animal foods, Trichoptera larvae in particular, were important in winter.(4) Analysis of the variation in the composition of the diet with age revealed several trends, notably a decrease in the importance of plant material, aquatic and aerial insects with age and a corresponding increase in the importance of larger prey foods such as fish, frogs and crayfish.(5) The commonly held view that chub are deleterious to salmonid stocks was examined. The absence of direct predation and the small likelihood of direct competition suggests that this view is incorrect.