Effects of water-level fluctuations on the environmental characteristics and fish-environment relationships in the littoral zone of a reservoir

Abstract

Water-level fluctuations are a major function of reservoirs that influence the littoral zone of the lake, and prove to be of high importance for the whole biological communities of lakes. Working on a French hydropower reservoir, we studied the influence of water-level fluctuations on intra-annual variations of littoral habitat availability and their consequences for the structure of fish assemblages inhabiting the littoral zone. As the water level decreased significantly, habitat conditions tended to be much more homogeneous. The proportion of sites with a thin substrate and low slope increased, while submerged vegetation and riparian shade disappeared. The relationship between habitat complexity and fish assemblage changed along the water-level gradient. The habitat effect on assemblage structure was strongest when the water-level conditions were high and very high, and weaker for low and very low water-level conditions. A homogenization of fish assemblages was observed when the water-level condition reached a threshold. These results suggest an effect of water-level management in structuring fish assemblages of the littoral zone of a reservoir due to a decrease of habitat complexity.

Habitat use and preference of adult perch (Perca fluviatilis L.) in a deep reservoir: variations with seasons, water levels and individuals

“…These results, based on the entire lake, are in agreement with other studies (Gasith & Gafny, 1990;Gasith & Gafny, 1998), and mean that lowering WL correspond to fewer refuge areas and probably fewer food resources for perch (Zohary & Ostrovsky, 2011;Zohary & Gasith, 2014). They also confirmed the trends observed by Logez et al (2016) with a point sampling on the same lake, but brought additional information as the stable availability of littoral tree stumps with WL and the rise of the relative availability and surface of the littoral area when the WL dropped.…”

“…In the same reservoir in summer and autumn, Logez et al (2016) observed that the littoral fish assemblages, composed of juveniles and adults, were dependent on the WL and tended to homogenize when the habitat complexity lowered, suggesting variations in habitat use when its availability changed, even if adults seemed to be the less affected. Considering the advantages of the littoral zone for fish fauna (Schiemer et al, 1995;Schmieder, 2004;Lewin et al, 2014) and the importance of the habitats impacted by WLF for perch (Imbrock et al, 1996;Zamora & Moreno-Amich, 2002;Pekcan-Hekim et al, 2005;Cech et al, 2009;Muska et al, 2013), we expected some changes in the habitat preferences at different WL.…”

“…Though, main annual features emerge. In spring, the high WL is from far the most frequent whereas the low one is in autumn because, at the beginning of this season, the WL is usually lowered in anticipation of rains (Logez et al, 2016).…”

“…The reservoir is located in a rural and natural environment, in a forest land cover dominated catchment with low anthropogenic activities (Logez et al, 2016). This reservoir, with a 229 km 2 watershed, is an impoundment of the Vezere River.…”

“…More specifically, studies have shown that WLF can affect various ecological aspects of fish species such as their growth, distribution and behaviour (e.g. Gaboury & Patalas, 1984;Rogers & Bergersen, 1995;Fischer & Ohl, 2005;Sutela & Vehanen, 2008;Logez et al, 2016). Indeed, WLF can lead to loss of potential prey (Winfield, 2004), loss of refuge areas (Kaczka & Miranda, 2014) and loss of spawning habitats (Hudon et al, 2005) for fish fauna.…”