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To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius), pikeperch (Sander lucioerca) and catfsh (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found signifcant diferences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfsh frequently visited a tributary during the warm season (late spring and early autumn), and moved closer to the dam during the cold season (late autumn to early spring). Pike longitudinal activity was highest in the cold season, pikeperch in the warm season, and catfsh activity peaked in both seasons. Overlap in the depth use among species was higher in the warm season, when all species used the upper layer of the water column, and lower in the cold season, when pikeperch and catfsh used deeper areas. These results demonstrated overlay and temporal variation of habitat use among these predators, as well as potential spatiotemporal space for their direct ecological interactions. Acoustic telemetry · Predators · Habitat use · Movement ecology · Winter ecology more...

Fish respond to predation threat by size/cohort-dependent presence in particular habitats and this may contribute to sexual segregation between habitats in species with sexual size dimorphism (SSD). The present study examines the validity of the “predation risk hypothesis” and importance of SSD on habitat (pelagic/inshore) segregation and dietary differences between sexes in three cyprinids with various magnitudes of SSD-roach (Rutilus rutilus), freshwater bream (Abramis brama) and bleak (Alburnus alburnus). Fish were sampled using gillnets over five consecutive years in the Řimov Reservoir. Habitat segregation with female overrepresentation in the pelagic habitat was found in the most sexually dimorphic species with 26% bigger females—the roach. When analysis of habitat segregation was size-controlled, this segregation ceased to confirm the importance of SSD. Freshwater bream sexes (2% SSD) differed in diet but did not differ in habitat occupation. Bleak sexes were not segregated. Larger roach individuals (predominantly females) are less threatened by gape-limited predators and consequently they can occupy the risky but optimal (for zooplankton acquisition) pelagic habitat. Our results demonstrate that habitat segregation is present in the species with the most pronounced SSD. more...

We investigated diel habitat use of fish covering the littoral and pelagic zones of the Řimov Reservoir (Czech Republic) and analyzed the influence of predator presence and of shifting feeding habitats in all dominant species and age groups. Our sampling revealed distinctive diel changes of fish distribution in the reservoir, which were age- and species-dependent. The overall abundance of subadult fish in littoral habitats was significantly higher at night than during the daytime. Subadults were almost absent in pelagic habitat during the day and their presence increased during the night, although densities were smaller than in the littoral. Adults preferred the pelagic zone during the day and partly migrated to the littoral at night. Potential fish predators were most likely responsible for small fish avoidance of the littoral and pelagic zones during day. Higher availability of food in the littoral was the most important driver of the high occurrence of subadults at night. Day preference of pelagic zone by adults is most likely caused by higher profitability of this habitat in comparison with littoral. The reasons for night inshore migration of adults are not obvious, but the homogenization of their distribution or resting in the littoral could explain such behavior. more...