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.
Differences in growth of perch ( Perca fluviatilis L.) in two small forest lakes
Growth patterns and food composition of perch, Perca fluviatilis L., was studied in two small forest lake populations in southern Finland. Size and morphometry of the lakes and physical and chemical properties of water are similar. There is a clear difference in the growth rates of perch between the two lakes. The difference in growth is highly significant in all age groups. In the first lake there is a perch population of 2 000 (1 750 ind • ha-1) adult fishes. In the second lake there is a small population of pike, that keeps the perch population down: 200 adult perch (530 ind • ha-1). The main food items of perch are crustacean zooplankton, Asellus aquaticus L. and Trichoptera larvae in the first lake and zooplankton, Odonata larvae, Ephemeroptera larvae and Heteroptera in the second. It is concluded that the main reason for the growth difference of studied perch populations is the different population density. There are also differences in species composition of bottom fauna of the lakes, maybe owing to the floating Sphagnum peat moss vegetation in the second lake. This can also affect the growth difference between the two populations of perch.
Biodiversity, conservation, and sustainable development
This important book highlights the conflicts between economic growth and the conservation of nature in the context of sustainable development. It places particular emphasis on biological diversity and examines possible policies for resolving conflicts which arise from the contrasting goals of conserving the natural environment and economic growth.