Movement Behaviour of Three Rheophilic Cyprinids in a Culvert‐Fragmented Stream

Many freshwater fish species rely on movement across unobstructed river systems to complete their life cycles. However, anthropogenic activities such as river regulation, dams, and culverts increasingly restrict fish movements by compromising river connectivity and altering habitat characteristics. This study aimed to assess the effect of habitat modification and a 76 m long culvert on the movement of three rheophilic cyprinids (common barbel Barbus barbus , European chub Squalius cephalus , and common nase Chondrostoma nasus ) in the River Geul, a chalk stream in the Netherlands. We hypothesised that (1) most habitat use would be observed upstream of the culvert, (2) interspecific variation in culvert passage rates would be present because of differences in movement timing throughout the diurnal cycle, where least effects of culvert fragmentation were expected on more nocturnally active species such as the common barbel, and (3) the culvert would affect larger, adult individuals the least, due to their increased swimming capabilities and larger home ranges. Radio‐frequency identification (RFID) telemetry data obtained with passive integrated transponders (PIT tags) revealed significant discrepancies in habitat use among river sections, where all three species occurred most in the more natural, upstream sections of the river. Passage rates of the culvert were high, and passage did not differ between species with varying diel timing of movement. However, larger individuals that had been tagged for a longer time were generally more likely to pass through the culvert. We conclude that habitat modifications and the construction of migration barriers resulted in the increased occurrence of three rheophilic cyprinid species in the more upstream, natural sections of a chalk stream, and that these anthropogenic activities therefore likely restrict the extent of available suitable habitat.