The population density of perch, Perca fluviatilis L. in the Cikola backwater system of the river Danube, Hungary
The numbers of perch Perca fluviatilis in the Cikola backwater system of the river Danube were estimated by mark-recapture techniques using multiple fishings. Fish were caught by fyke nets and electrical fishing. The latter method was unselective for sex and the catch data could be used to correct the sex bias in the fyke net catches. A population estimate in April of 6059 ind ha−1 (95% C.L. 5135–7386) for perch > 5 cm was obtained for a 0.6 ha area of backwater and 1665 ind ha−1 (95% C.L. 1204–2692) in May for a 0.4 ha area of a small bay.
An empirical model for predicting microhabitat of 0+ juvenile fishes in a lowland river catchment
SummarySpecies-habitat relationships are an important aspect of fish life history, particularly in early ontogeny. To address the lack of information on the microhabitat use/requirements of European coarse fishes, particularly 0-group fishes in riverine systems, an empirical model was generated from data collected in the River Great Ouse catchment (UK). During 7 weeks in autumn 1990, data on young-of-the-year (0+) juvenile fishes and 15 environmental variables were collected at 2800 stratified, random point samples within 130 study sites (streams, rivers, side-channels, backwaters). Of 24 species of 0+ fish, only 10 were captured in ≥ 3% of non-null samples. Association analysis and canonical correspondence analysis of the samples-by-species (967×10) and samples-by-variables (967×15) data matrices revealed that the shallow, narrow, lotic, stony-pebbly channel microhabitat of riffles and runs was preferred by the progeny of substrate-spawning, substrate/plant-spawning and nest-guarding fishes. Moderately deeper and wider, sinuous channels, with slowto-moderate water velocities and medium-sized substrata were also favourable to progeny of substrate spawners. Assemblages of 0+ fish in deeper, wider, silted, trapezoidal-shaped channels with slow-to-lentic flowing water, i.e. channelised and regulated, were dominated by ubiquitous (plant/substrate) spawners.
The Growth and Mortality of Four Species of Fish in the River Thames at Reading
This paper results from a series of observations made on fish populations in the River Thames at Reading between October 1958 and October 1959. The work forms part of a long-term ecological investigation being carried out in the Caversham-Sonning reach of the river. The four species being discussed in this paper are roach-Rutilus rutilus (L.), bleak-Alburnus alburnus (L.), dace-Leuciscus leuciscus (L.) and perch-Perca fluviatilis L. These four species comprised 91 %Y of the total catch and estimates of their population densities have been reported (Williams 1965). The stock densities recorded were extremely high and the present study on growth and mortality is a necessary step in the evaluation of both the interrelationships within the community and those between the community and its environment. Very few population studies have been made of coarse fish in Britain, especially from rivers. For some species, however, there are published data on growth in various habitats which may serve to indicate whether or not the Thames fish are stunted. Only for perch is there comparable work on both growth and mortality in another habitat (Le Cren 1958).