“…According to this researcher, although predators be successful in high-visibility environments, predation rates may also be higher in places with lower visibility, but with high abundance of prey. Similar to São Simão, greater species richness has been reported in the riverine zone of other Brazilian reservoirs (Oliveira et al, 2004;Gubiani et al, 2010;Terra et al, 2010) as well as in reservoirs of other countries (Gido et al, 2002;Prchalová et al, 2009;Freedman et al, 2013). The riverine zone can be considered a quasi ecotone, because of the overlap of fluctuating riverine and lacustrine conditions .…”
Section: Effect Of Reservoir Zone On Fish Assemblage Compositionmentioning
“…According to this researcher, although predators be successful in high-visibility environments, predation rates may also be higher in places with lower visibility, but with high abundance of prey. Similar to São Simão, greater species richness has been reported in the riverine zone of other Brazilian reservoirs (Oliveira et al, 2004;Gubiani et al, 2010;Terra et al, 2010) as well as in reservoirs of other countries (Gido et al, 2002;Prchalová et al, 2009;Freedman et al, 2013). The riverine zone can be considered a quasi ecotone, because of the overlap of fluctuating riverine and lacustrine conditions .…”
Section: Effect Of Reservoir Zone On Fish Assemblage Compositionmentioning
“…In late spring and early summer, the open water of many deep, thermally stratified European lakes and reservoirs is occupied by young‐of‐the‐year European perch ( Perca fluviatilis : Percidae, L.), a widely distributed species that accounts for a considerable proportion of pelagic early juveniles communities (Čech, Kubečka, Frouzová, Draštík, Kratochvíl, & Jarošík, ; Jůza et al., ; Probst, Thomas, & Eckmann, ; Vašek et al., ; Vejřík, Matějíčková, Jůza, et al., ; Wang & Appenzeller, ). Perch early juveniles (larvae and juveniles till the metamorphosis when fish started to be fully pigmented with individual fins fully developed) were observed to split into vertically separated communities (epipelagic, bathypelagic) in which spatially and temporarily distinct bathypelagic early juveniles migrated vertically as part of their antipredatory behaviour.…”
Section: Introductionmentioning
confidence: 99%
“…The reservoir has served as a freshwater store for České Budějovice and adjacent localities (Říha et al., ). The local early juveniles communities are dominated by cyprinids but percids, particularly perch and pikeperch ( Sander lucioperca : Percidae, L.), are also important components (Jůza et al., ; Jůza et al., , Jůza et al., ). During the daylight hours, the most common piscivorous fish species in the open water of the Římov Reservoir are adult perch and asp ( Aspius aspius : Cyprinidae (L.)) (Vašek et al., ).…”
Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood.
Undertaking a large‐scale field experiment in a thermally stratified, canyon‐shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour.
Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (depth >3.0 m) reaching a maximum amplitude of 13 m.
Hydroacoustic recordings by the echosounder SIMRAD EK 60 (120 and 400 kHz) showed that during the experiment, when the surface was covered with a large black non‐transparent foil (2500 m2; simulated conditions of complete and constant darkness), the regular vertical movement of the bathypelagic perch early juveniles was interrupted and the community occupied the epilimnion constantly for 24 hr.
Immediately after the foil was removed at midday, the bathypelagic perch early juveniles were exposed to a steep increase in light intensity (from <1 LUX to >100 × 103 LUX) and they escaped into the hypolimnion where they were safe from visual predation which took place in the bright surface layers (epilimnion particularly). Our findings imply that occupying a deep, dark refuge in the daytime is essential for the survival of perch in their early life stage.
“…It is a canyon-shaped reservoir with a total length of 12 km, a maximum volume of 33 × 10 6 m 3 , a surface area of 2.1 km 2 , and an average and maximum depth of 16 m and 45 m, respectively. The trophic state of the reservoir is mesotrophic to eutrophic with the dominance of common bream, roach and bleak in both juvenile and mature fish communities 19, 50 . Due to the strong temperature and oxygen vertical gradients during summer months, both juvenile and adult fish inhabit the water layer above the thermocline 4, 19, 32 .Figure 7A map of the Římov Reservoir and location in the Czech Republic.…”
For ethical reasons and animal welfare, it is becoming increasingly more important to carry out ecological surveys with a non-invasive approach. Information about fish distribution and abundance in the upper water column is often fundamental. However, this information is extremely hard to obtain using classical hydroacoustic methods. We developed a rigid frame system for pushing upward looking transducers of the scientific echo sounder (38 and 120 kHz) in front of the research vessel. The efficiency of the new approach for monitoring juvenile fish at night was investigated by comparing the results with a quantitative fry trawl in the Římov Reservoir in the Czech Republic. The experimental setup enabled comparisons for the 0–3 m and 3–6 m depth layers, which are utilized by almost all juvenile fish in summer. No statistically significant differences in the estimated abundance of juveniles were found between the two sampling methods. The comparison of abundance estimates gathered by the two frequencies were also not significantly different. The predicted mean lengths from acoustic sampling and the trawl catches differed by less than 10 mm in all comparisons. Results suggest that mobile hydroacoustic upward-looking systems can fill the methodological gap in non-invasive surveying of surface fishes.
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