The effect of depth, distance from dam and habitat on spatial distribution of fish in an artificial reservoir

Abstract –  Spatial distribution of the fish community in the deep canyon-shaped Římov Reservoir, Czech Republic, was studied using overnight gillnetting fishing in 1999–2007. Effects of depth, distance from the dam to the tributary and habitat type (benthic and pelagic) on fish community structure, catch per unit of effort (CPUE), biomass per unit of effort (BPUE) and average weight were tested. Fish were recorded in all sampled depths and parts of the reservoir. Redundancy analysis revealed that effects of three environmental variables were significant and most variability was explained by depth, then by distance from the dam and habitat type. CPUE and BPUE of all species decreased with depth and responses of individual species to depth were similar for juvenile and adult fish. Number of species, CPUE and BPUE of all species except perch increased heading towards the tributary and peaked close to or at the tributary part of the reservoir. Responses of juvenile fish to distance from the dam differed from that of adult fish. Structure of fish community differed in benthic and pelagic habitats with species preferably occupying epipelagic (bleak, asp, rudd and juvenile bleak, roach and bream) or littoral waters (perch, pikeperch, ruffe, roach, bream and juvenile percids). This study showed that fish distribution in the reservoir followed distinct patterns, which were probably shaped by a combination of physiological constraints plus trade-off between food resources and competition.     

Functional vs scenic restoration – challenges to improve fish and fisheries in urban waters

Abstract Two rehabilitation projects were compared to determine their feasibility for successfully improving habitat for fish in urban waters. The first re‐meandering project involved channel reconstruction in the Müggelspree upstream of Berlin to create an aesthetically pleasing, stable, meandering channel. The second project addressed a typical habitat bottleneck for fish found in urban waterways; that of nursery habitats lost due to river engineering works. Rehabilitated and control sites were sampled before and after in the Müggelspree and once in the urban Spree River. A total of 30 303 fish belonging to 27 species were collected. The fish assemblage was dominated by generalist species with 81% roach, Rutilus rutilus (L.), and perch, Perca fluviatilis L. Species diversity did not improve in either the rural or urban stretch. In the Müggelspree, the loss of riverine habitats was mirrored by significant declines in the densities of chub, Leuciscus cephalus (L.), ide, Leuciscus idus (L.), gudgeon, Gobio gobio (L.), rheophilic and lithophilic species. By contrast, densities of rheophilic species around the artificial structures created in the urban Spree River, although the main effect was an overwhelming increase in roach and perch. The results suggest that if underlying bottlenecks can be identified, artificial structures can provide functional fish habitat that replaces the natural equivalent in urban river stretches. Consequently, even the most heavily degraded waters provide opportunities to improve fish diversity and fisheries using artificial habitat structures.     

The use of two nature-like fishways by some fish species in the Swedish River Emån

Abstract –  We studied the use of two nature-like fishways by 15 fish species ( N  = 240) in the River Emån in southern Sweden. Use of the fishways for both passage and as a habitat was studied by electrofishing, trap catches and PIT telemetry. Of the 187 PIT-tagged fish, 52 individuals from 10 different species ascended one of the fishways for a total passage efficiency of 74%. For the five species that most frequently ascended the fishways, the passage efficiency was 100% for tench ( Tinca tinca L.) and perch ( Perca fluviatilis L.), 86% for chub ( Leuciscus cephalus L.), 60% for burbot ( Lota lota L.) and 50% for roach ( Rutilus rutilus L.). Individuals that failed to pass the fishways were typically small cyprinids or species that were assumed to have taken up residence in the fishways, such as juvenile brown trout ( Salmo trutta L.) and burbot. The nature-like fishways have re-established longitudinal connectivity for most of the studied species and also functioned as rearing and winter habitat for a number of species.     

A test of crayfish predatory and nonpredatory fish species as bait in crayfish traps

The effectiveness of different crayfish: predatory (pike, Esox lucius L., perch, Perca fluviatilis L.) and nonpredatory [roach, Rutilus rutilus (L.) , and bream, Abramis brama (L.)] fish species as bait for noble crayfish, Astacus astacus L., was tested. Trapping was conducted in two lakes in Norway and Lithuania. Nonpredatory bream and roach were superior as noble crayfish bait compared with predatory perch and pike. In the Norwegian lake bream was also superior to roach. Pike- and perch-baited traps tended to catch larger crayfish than bream- and roach-baited traps. An alarm or avoidance response to different live or dead fish predators (e.g. pike or perch) might exist and could be more pronounced in smaller crayfish, thus explaining that pike and perch as bait catch fewer and larger crayfish. Another explanation could be that the odour of pike and perch flesh is simply less attractive or diffuses more slowly through the water. Selecting the most efficient bait will increase the catch per unit effort (CPUE); in this study there was a four-fold variation in CPUE between the best and worst bait type. In test-fishing/monitoring surveys it is important to standardize the bait type used.     

Recruitment patterns of six species of cyprinid fishes in the lower River Trent, England

Abstract – Fisheries data were collected for six species of 0-group cyprinid fishes from eight sites in the lower reaches of the River Trent, England, between May and October 1999 inclusive, using a micromesh seine net. Recruitment and growth patterns were observed via monthly length–frequency histograms and estimations of mean length. In the cases of roach and dace, growth was approximately linear through the summer, before declining in September and October. In the cases of chub and gudgeon, and to a lesser extent bream and bleak, however, there were suggestions of multiple recruitment events. It is argued that some of the fish species examined in the present study adopt fractional or protracted spawning strategies in the lower River Trent.     

Fish pass effectiveness for bullhead (Cottus gobio), perch (Perca fluviatilis) and roach (Rutilus rutilus) in a regulated lowland river

Abstract –  The effectiveness of a pool-and-weir fish pass in the regulated river Laarse Beek (Belgium) was assessed for bullhead ( Cottus gobio ), perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) from August 2002 to April 2003. Fish were caught by electrofishing downstream, within and upstream of the fish pass. They were marked with visible implant elastomer tags and released downstream of the fish pass. Our results suggest that the fish pass is ineffective for the bullhead because none of the 1270 tagged bullheads were recaptured in the upstream study area. Passage failure most likely resulted from excessive water velocities in the fish pass. On the contrary, 8% of the tagged perch and 29% of the tagged roach were recaptured in the upstream study area. Several management strategies are proposed to allow free upstream passage of the endangered bullhead at the fish pass under study.     

Seasonal and diurnal variation of downstream fish movement at four small-scale hydropower plants

Hydropower structures hinder the movement and migration of fishes, impairing their life cycles. Additionally, downstream moving fish are often at risk of being injured during turbine passage. To improve hydropower production towards more fish-friendly techniques and management, knowledge on timing and extent of natural patterns of fish downstream movement is necessary. So far, migration behaviour of long-distance migrators such as eel or salmon has been well studied, but little is known about seasonal and diurnal movement patterns of nonmigratory species or medium-distance migrators. In this study, movement patterns of 39 fish species captured by stownets while transiting hydropower facilities in four impounded rivers were assessed and compared with the fish community composition directly upstream of the hydropower plants assessed by electrofishing. Strong differences between the fish community composition inhabiting the upstream sides of the dams and the fish detected in downstream passage were evident. In each study river, the downstream moving fish community composition differed significantly between spring and autumn. On average, significantly more fish were caught during the night (2.9 fish/hr) than during the day (1.3 fish/hr). Topmouth gudgeon, European grayling and pike-perch mostly moved downstream during the night, whereas roach, spirlin and bleak were the most frequent downstream moving fish during daytime. Downstream fish movement was positively related with turbidity, water temperature and discharge. The strong differences in seasonal and diurnal fish movement patterns suggest that fish damage can be strongly reduced by adaptive turbine and corridor management, for example by shutting down turbines at peak movements.     

The Effects of Water Temperature and Flow upon Angling Success in the River Severn

Angling catch data was gathered by a postal questionnaire system from angling clubs holding competitions in three sections of the River Severn over a period of 3 years (1975–78). Angling success was measured as the percentage of anglers taking part that caught fish and as the overall catch rate (g/man/h) of the competing anglers. Species composition of the catch was also recorded. Angling success was closely related to water temperature. Parabolic regressions were fitted to the data. Optimum temperatures for angling success were between 18 and 20°C, except for the Lower Severn section where maximum catch rates were achieved at 14.9°C. Flow had little effect upon angling success until a critical flow was reached, above which success was considerably reduced. Critical flows for the upper, mid and lower sections were approximately 3,000, 5,000 and 10,000 Ml/day, respectively. Species composition of catches within river sections was influenced by water temperature. Some species (bleak, bream, dace and eels) were relatively more abundant in catches made at high temperatures whilst others (chub and roach) predominated at tow temperatures. It is suggested that the percentage of anglers catching fish is the most reliable indicator of angling success.     

Distribution and feeding of juvenile fish on invertebrates in littoral reed (Phragmites) stands

Abstract – Complex interactions between fish predators and their prey have been found in structurally complex habitats built by submerged macrophytes. In contrast, the role of comparably structured littoral reed stands in shaping biotic interactions has not been investigated. We hypothesised that reed stands may be a valuable feeding habitat for juvenile fish, and that perch and roach may segregate along the spatial and dietary niche dimensions between reed and open water habitats. In contrast, the protection effect of reed against predators was assumed to be rather low because of the lower plant volume infested in reed when compared with submerged macrophytes. We analysed biomass and growth of juvenile (age 0 and age 1) perch and roach in littoral reed habitats and in open water habitats in front of the reed in the shallow Lake Müggelsee over 4 months in 2000. Sampling was conducted by point-abundance electrofishing over the full diel cycle (day, dusk, night, dawn). Zooplankton and benthos biomasses were determined in both habitats as well, and habitat-specific diet of fish was assessed during day and night. Roach were more frequent than perch in both habitats. Food of roach included a higher proportion of zooplankton, whereas perch fed more on macroinvertebrates. Overall, diet overlap between the fish groups was high. Diel distribution of fish did not follow the expectations of habitat segregation between perch and roach. Instead, the function of reed as refuge habitat against littoral piscivores (mainly birds) may have caused the strong daytime preference for reed in almost all fish groups, which was partly upset by roach at night. The higher behavioural plasticity of roach may explain their good performance even under the conditions of high structural complexity.     

Larval and early juvenile fish dynamics in main channel and backwater lake habitats of the Illinois River ecosystem

The spatial and temporal complexity of large river ecosystems likely promotes biological diversity within riverine larval fish assemblages. However, the focus of most previous riverine studies of larval fish distribution has tended to concentrate mainly on backwater habitats. There has been less focus on the value of the main channel for larval fishes. We sampled two habitats types (three main channel sites and three backwater lakes) along 20 km of the Illinois River ecosystem during 2 years to compare the larval fish distribution along both spatial and environmental gradients between these habitats. Across the 2 years of this study, we found similar trends in the spatial and temporal distribution of larval fish, although there were some differences in densities between years. The relative abundance and size of many of the different fish taxa varied among habitats. Centrarchids, clupeids, poeciliids, cyprinids (excluding common carp) and atherinids were more abundant within backwater lake habitat. In contrast, common carp (Cyprinus carpio), sciaenids, moronids and catostomids were more abundant in main channel habitats. Furthermore, sciaenid and clupeid larvae captured in the backwater lake habitat were larger as the season progressed than those captured in the main channel. Our study suggests that larval fish show habitat specialisation, similar to adults, indicating that both the backwater lakes and the main channel are both important for larval fish and preserving the diversity of the fish assemblages in large floodplain rivers.