Longitudinal and Vertical Spatial Gradients in the Distribution of Fish within a Canyon‐shaped Reservoir

Abstract

The large-scale spatial distribution of fish was investigated within a morphometrically simple canyon-shaped reservoir with a single major tributary and a longitudinal trophic gradient (Římov Reservoir, Czech Republic). Samples of fish were taken by Nordic survey gill nets (several mesh sizes from 8 to 70 mm knot to knot) installed as surface nets at several offshore areas located along the longitudinal axis of the reservoir. Surveys were carried out in late summer during 1999-2003. An obvious distribution gradient of fish was revealed along the longitudinal axis of the Římov Reservoir. The total relative fish abundance and biomass (catch per unit effort) decreased considerably from the upstream end of the reservoir toward the dam. Roach (Rutilus rutilus), bleak (Alburnus alburnus) and bream (Abramis brama) comprised the bulk of catches at all areas. Enhanced dominance of bream was observed in the fish assemblage at the uppermost, more eutrophic area of the reservoir. The highest number of fish species and the highest abundance of young-of-the-year fish were also observed in the tributary area. In the downstream part of the reservoir, gill net surveys along the vertical depth profiles indicated that offshore fish occupied mostly the epilimnion. Extreme flood events affected the Římov Reservoir, however, it seemed they had no significant impact on the gradients described.

Daphniahybridization along ecological gradients in pelagic environments: the potential for the presence of hybrid zones in plankton

“…Fish predation pressure physically limits the size of Daphnia occurring in different parts of the water body, and only when the predator pressure is relaxed under a certain threshold does interspecific competition among larger taxa come into play. Fishes are preferentially present in the upstream reservoir regions ( Vašek et al 2004); this fact is reflected in the small size of Daphnia present there (figure 4). The tendencies in longitudinal arrangement of the taxa from the hybridizing pair D. galeata-cucullata agree well with significant differences in carapace size of the respective taxa, favouring the smallest Daphnia upstream.…”

Hydroacoustic estimates of fish stocks in temperate reservoirs: day or night surveys?

“…Fish species in manmade reservoirs have rarely been observed below the thermocline during summer thermal stratification (Kubečka and Wittingerová 1998;Matthews et al 2004;Vašek et al 2004;Järvalt et al 2005), except for larval and juvenile perch (Čech et al 2005). Diel vertical migration was not observed at the studied reservoirs, most likely because strict temperature and oxygen stratification of the water column prevent fish from swimming to deeper layers.…”

“…22, 69-77 (2009) Usually, fish are not distributed randomly in reservoirs. Reports of longitudinal (tributary-dam) and vertical gradients of fish abundance and biomass have been made for many European and American reservoirs (Aglen et al 1999;Vašek et al 2003;Matthews et al 2004;Vašek et al 2004;Draštík et al 2008;Prchalová et al 2008). Also the horizontal pattern (offshore-inshore) in fish distribution is nonrandom and could be species specific (Gauthier and Boisclair 1997;Jeppesen et al 2006).…”

Longitudinal patterns of phytoplankton distribution in a tributary bay under reservoir operation

“…Along with the transport and sedimentation of influent materials, the important hydrodynamic characteristics dominating the reservoirs' spatial distribution such as river inputs, advective flow regimes, and regulated outflow provide a physical setting that fosters the establishment of physical, chemical, and biological longitudinal spatial gradient from headwaters to dam in the main axis of the reservoir (James et al, 1987). The physical and chemical gradients imposed by a river flow is a typical feature in deep valley reservoirs (Vasek et al, 2004), whereas the advective flow regimes and regulated outflow are obviously under the impact of reservoir operation. The reservoir operation distinguishes the reservoir from other natural aquatic systems, intended to guide real-time operation management so that the releases made are in the best interests of the system's objective consistent with certain inflow and existing storage levels (Malekmohammadi et al, 2009).…”