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.
Assessment and control of non‐indigenous brown bullhead Ameiurus nebulosus populations using fyke nets in shallow ponds
In order to evaluate fyke nets as a tool for population assessment and mass removal of brown bullhead Ameiurus nebulosus populations, small, shallow ponds were sampled during late summer in 1999 and 2000. Catch efficiency, species and size selectivity of fyke nets were investigated with the mark-recapture method. Two different strategies were applied: (1) on six occasions, the mark-recapture method was applied to entire populations, and (2) in six other cases, sampling was done in two replicated enclosed areas (625 m 2 ). When applied to entire populations, fyke nets were found to be size selective, and capture efficiency significantly increased with standard length. Conversely, no size selectivity of fyke nets was found in enclosed areas. Sampling in replicated enclosures yielded reproducible estimates of population density and biomass. The results suggest that double fyke nets, when combined with the mark-recapture technique, are a very useful tool for the efficient and reliable assessment of brown bullhead populations. The results of the study also suggest that double fyke nets may potentially be a cost-effective tool for the mass removal of non-indigenous brown bullhead populations.
Species Interactions in Percid Communities
Evidence for species interactions in communities with Perca and Stizostedion is evaluated. Substantial evidence exists for the importance of predation by and on percids to community structure and function. Some evidence also clearly demonstrates that competition is an important interaction both within Perca populations and between Perca and other species. The necessity of using manipulative experiments to test for community level effects of competition and predation is emphasized. Such manipulative experiments, however, should be restricted in number and conducted with great care, because the community changes they induce are often irreversible and detrimental.Species interactions related to feeding have apparently resulted in the partitioning of habitat and food resources among fishes in percid communities. Partitioning of space is considered in terms of distribution of Perca and Stizostedion in respect to temperature in stratified and unstratified aquatic systems. In stratified lakes, percids are expect...