Publication Abstract

Consistency of diel behaviour and interactions of stream fishes and invertebrates during summer

G.H. Copp, S. Spathari and M. Turmel

We examined the diel dynamics of fish and invertebrates during summer in the River Lee, a mesotrophic chalk stream in Hertfordshire, England, and in particular the consistency of patterns observed over three 24-h cycles within a 10-day period in summer (28-29 July, 4-5 and 7-8 August 1997). We tested for temporal variations in epibenthos density and population size structure as well as age-specific fish density, microhabitat use and contagion. We also tested for correlations between the number of prey items in fish guts per mm fish standard length (SL), a surrogate of foraging success, and fish density in point samples (an estimator of shoal size). Consistent patterns were observed in invertebrates and fish, though variability was greater in the former. Epibenthic invertebrates (except Chironomidae) demonstrated few or no diel differences in density, but some differences in size (based on head widths) were found in larvae of Chironomidae and Ephemeroptera (mainly Baetis rhodani and Ephemerella ignita) between times of day. Over the three diel cycles, fish density varied consistently and diel variations were observed in fish shoaling behaviour, habitat use, prey size and prey composition. Prey numbers (per mm SL) in the gut generally decreased with increasing shoal size, but this was significant in Gobio gobio only. Prey numbers in the gut were correlated in some cases with habitat variables, in particular with the distance fish were captured from the bank. Despite relatively low epibenthic densities, Chironomidae larvae were a prominent and preferred feature in the diet of all fish species, followed by Ephemeroptera in some fish (0+ Barbus barbus, 0+ and 1+ Barbatula barbatula, 1+ and =2+ Cottus gobio) and Simulidae in others (0+ and =1+ G. gobio, 0+ Leuciscus cephalus, 0+ and 1+ Phoxinus phoxinus), with Trichoptera larvae, Asellus sp., Ostracoda and Annelida tertiary prey taxa. The relatively consistent diel patterns observed over the replicate 24-h samplings suggest that data from single 24-h cycles can be representative and that day-time only surveys of European riverine fishes may give unreliable estimates of fish size and abundance.

Reference:

G.H. Copp, S. Spathari and M. Turmel, 2005. Consistency of diel behaviour and interactions of stream fishes and invertebrates during summer . River Research and Applications, 21: 75-90.