Openness of Fish Habitat Matters: Lake Pelagic Fish Community Starts Very Close to the Shore

Abstract

Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic community was observed only in the first pelagic gillnet above the bottom depth of 3.5 m. Open water catches were relatively constant with small signs of decline towards the middle of the lake. The results indicate that the benthic gillnet catch is representative of a very limited area and volume, while most of the volume is dominated by the pelagic community. This has important consequences for the assessment of the community parameters of the whole lake following the European standards for gillnet sampling design.

Long-term monitoring of fish in a freshwater reservoir: Different ways of weighting complex spatial samples

“…The depth of the stratum is the difference between the depth boundaries of two successive strata. Benthic volume was consistent with the results of Moraes et al (2021) and was defined as the layer 1.5 m above the bottom within each stratum. All remaining volume in each depth stratum was considered pelagic.…”

“…As expected, the three methods used to calculate the reservoir-wide relative abundance and biomass of the dominant species and the total fish community produced different VPUEs (Figures 2, 3). The CEN protocol places the greatest emphasis on benthic habitats, which generally harbor higher fish abundance, biomass, and species richness than pelagic habitats (Prchalová et al, 2008;Prchalová et al, 2009b;Moraes et al, 2021). Consequently, it provided higher reservoir-wide CPUEs and BPUEs by a factor of two when estimates are compared to the two volume-weighting approaches (Table 3).…”

“…The reservoir harbors more than 40 freshwater fish species belonging to 15 families (Table 1), including Acipenseridae, Anguillidae, Centrarchidae, Cottidae, Cyprindae, Esocidae, Gobionidae, Leuciscidae, Nemacheilidae, Percidae, Petromyzontidae, Salmonidae, Siluridae, Tincidae, and Xenocyprididae (Hladík et al, 2008;Prchalová et al, 2009b;Šmejkal et al, 2015;Blabolil et al, 2021). As shown in Table 1, about a quarter of the species are non-native species (Musil et al, 2010).…”

“…Fish assemblages of pelagic habitats in reservoirs are generally less diverse than those of benthic habitats. There are no truly pelagic fish species in Římov Reservoir, and the pelagic habitat is dominated by eurytopic species such as bleak, bream, roach, asp, and pikeperch (Moraes et al, 2021). Bleak is a highly successful species that dominates the pelagic habitat and thus the VOST and VOCOM species composition (Figure 4).…”

Living on the edge: Reservoirs facilitate enhanced interactions among generalist and rheophilic fish species in tributaries

“…While the main autochthonous primary production in rivers comes from benthic systems, primary production in reservoirs is mostly pelagic (Ward and Stanford, 1995). Littoral habitats with benthic food chains may be the most productive per unit area, but due to large pelagic spatial proportions of reservoirs, most production occurs in pelagic areas (Fernando, 1994;Moraes et al, 2021). The bulk of production in reservoirs goes from phytoplankton to zooplankton.…”