We studied movement and abundance of barbel, Barbus barbus , over three years (October 1995 to September 1998) in two stretches (Woolmer’s Park, Holwell Bridge) of a section of the River Lee (Hertfordshire, England) delimitated by water retention structures. Of 349 tagged individuals (168 at Woolmer’s Park; 181 at Holwell Bridge), 51.8 % and 13.3 % respectively were recaptured at least once, with a much higher rate of multiple recaptures at Woolmer’s Park, where monitoring of movements was over a longer period, than at Holwell Bridge, where too few recaptures were made for further movement analysis. At Woolmer’s Park, 77.1 % of the barbel showed limited (i.e. resident component) and the rest greater between- capture movements (i.e. mobile component). There was no preferential directional movement across size classes. Based on the available recapture data, population size (estimated through a Bayesian method) first increased moderately (1995–96) and then sharply (1996–97) at Woolmer’s Park, and even further later at Holwell Bridge (1998–99). This may reflect a recovery phase in the local population, or possibly a rising part of a cyclic recruitment pattern, such as reported for barbel elsewhere and for other cyprinids in the UK. Habitat enhancement is recommended over stocking, given the adequate abundance of barbel in areas with suitable habitat. However, it remains unclear whether fencing-off of the banks from livestock will enhance 0+ barbel numbers, which appear to be low relative to some European rivers of similar width and depth.
Size-frequency data were collected for two rheophilic fish species, Cottus perifretum and Leuciscus cephalus, at the confluences of 18 lowland tributaries along the regulated River Meuse (the Netherlands) between May 2004 and April 2005. Cottus perifretum is a resident species, using these stream mouth habitats throughout its entire life: i.e. as a spawning, nursery and adult habitat. Leuciscus cephalus is a transient species that uses these stream mouth habitats only as a temporary 0+ juvenile habitat during fall and early winter. This study suggests that the stream mouth habitats along the River Meuse fulfil different ecological functions for C. perifretum and L. cephalus.