Publication Abstract

Behaviour of young and small fishes in the River Lee (Hertfordshire) over a twenty-four hour cycle in midsummer

G.H. Copp

In a preliminary study of diel patterns in fish density and dispersion in a stretch of the River Lee, Hertfordshire, August 1996, data were examined with respect to time of day and in-stream location. Fish density, dispersion and the frequency of samples containing fish increased at night, the fish assemblage being comprised of minnow Phoxinus phoxinus, gudgeon Gobio gobio, chub Leuciscus cephalus, stone loach Barbatula barbatula, bullhead Cottus gobio, and barbel Barbus barbus, with a few specimens of three-spined stickleback Gaterosteus aculeatus occurring infrequently. Contagion in most species decreased at night, but minnow, stone loach and bullhead were the only species to demonstrate clear diel patterns in density. Fish densities and contagion in mid-channel reached their peak at dusk, whereas the highest densities at night were along the banks. The patterns observed here have been corroborated by subsequent investigations, but comparisons with published data under differnt moonlight conditions suggest that diel patterns in fish density are less clearly demonstrated in larger river systems, emphasizing the need for moonlight, prey and predator densities as well as other habitat characteristics to be taken into account when assessing diel patterns.

Reference:

G.H. Copp (2004) Behaviour of young and small fishes in the River Lee (Hertfordshire) over a twenty-four hour cycle in midsummer. The London Naturalist, 83: 87-96