Diel variation in habitat use by planktivores in field enclosure experiments: the effect of submerged macrophytes and predation


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The importance of submerged macrophytes and predation risk for habitat use by 0+ perch (Perca fluviatilis) and 0+ roach (Rutilus rutilus) was investigated in triplicate 78-m2 field enclosures with and without macrophytes in the middle. During three experimental runs, habitat use by fish were monitored every 6 h with Breder traps. Each period included 2 days of fish monitoring before stocking with piscivorous perch, and 2 days after. Predation risk significantly changed habitat use by 0+ perch in the morning, midday and evening, but not at night. By comparing with the unvegetated controls, we found a refuging effect of macrophytes in the morning. Under predation risk there was significant diel variation in habitat use by 0+ perch, suggesting a migration from the open water habitat at night into the macrophytes in the morning. Roach continued to use open water even after predators were stocked, but responded like perch by reducing overall activity.