Fish assemblage patterns in the littoral zone of a European reservoir

Abstract

1. Although reservoirs are common aquatic habitats in Europe, there is little quantitative information on the spatial organisation of fish assemblages inhabiting their littoral zones. Consequently, we characterised fish assemblage structure in the littoral zone of a reservoir (Lake Pareloup) in SW France during late spring, summer and early autumn (the growing season). 2. We measured the relative abundance of fish, weekly from mid-May to mid-October, using point abundance sampling by electrofishing. We identified temporal patterns in assemblage structure using hierarchical cluster analysis, and then characterised the spatial distribution of 17 defined ecospecies using a Kohonen self-organising map (SOM, an unsupervised Artificial Neural Network). 3. Our analyses revealed three distinct faunal structures within the littoral zone. From midMay to mid-July, adults and young-of-the-year (0+) occupied separate habitats, with most 0+ fish in vegetated habitats and adults in open water. From mid-July to late August, some 0+ co-occurred with adults, but most 0+ fishes remained in vegetated areas. Finally, from late August to mid-October, most fish (both 0+ and adults) left the vegetation for unvegetated littoral habitats, the exception being fish species known to be dependent on macrophytes. 4. Contrary to patterns for adult fishes, the 0+ fish assemblage was dynamic. These dynamics were driven by ontogenetic species-specific habitat changes. Consequently, there was little evidence of stable assemblages or strong assemblage-habitat relationships that would be expected of an 'interactive' assemblage. It is likely that the patterns observed are a result of species-specific response to habitat availability in the lake.

Patterns in diel habitat use of fish covering the littoral and pelagic zones in a reservoir

“…These ecospecies dominated in the pelagic zone and mostly avoided the littoral during the day. The observed day avoidance of shallow areas by large fish agrees with other studies from lakes, rivers, or reservoirs (Duncan & Kubečka, 1995;Wolter & Freyhof, 2004;Romare et al, 2003;Brosse et al, 2007;Erös et al, 2008) and seems to be a very common trend in freshwater ecosystems. The pelagic zone is suggested to be a more advantageous zone for large fish species because, contrary to small fish, they face a lower risk of predation in this zone (Werner et al, 1983;Lammens et al, 1992).…”

“…Moreover, such sampling could also reveal the occurrence of potential predators and evaluate their impact on the diel distribution dynamics of different species and size categories. In European freshwaters, studies dealing with diel changes of fish distribution largely focused on only one species (Schulz & Berg, 1987;Zamora & Moreno-Amich, 2002;Jacobsen et al, 2004) or sampling of a community in only one zone (Brosse et al, 2007;Erös et al, 2008). However, there is a very limited number of studies that performed simultaneous quantitative sampling of the whole fish communities in both zones and periods (Wolter & Freyhof, 2004;Muška et al, 2013) and in our best knowledge there is no study providing picture of diel changes among all mentioned habitats simultaneously.…”

Patterning and predicting aquatic insect richness in four West-African coastal rivers using artificial neural networks

“…Artificial neural networks are known as well-adapted tools for dealing with such problems and to extract information out of complex, nonlinear data. These methods are more and more used for patterning assemblages (Worner and Gevrey, 2006;Brosse et al, 2007;de Thoisy et al, 2008) and predicting occurrence and/or abundance of various taxa (Gevrey et al, 2005;Leprieur et al, 2006). The aim of our study was first to pattern aquatic insect distribution so as to determine characteristic assemblages for the different sites and rivers.…”

Spatio-temporal variations in abundance and assemblage patterns of fish larvae and their relationships to environmental variables in Sirindhron Reservoir of the Lower Mekong Basin, Thailand

“…Sampling was conducted on the day of full-moon in each month to avoid the influence of a lift net fishery where in lights used by fishermen during the new moon phase (Jutagate et al, 2003). Sampling was carried out in the littoral zone, as it is known to be the habitat preferred by larval fish (Brosse et al, 2007;Ríha et al, 2011). Maximum and mean depths of sampling sites were 1.07 and 0.48 m, respectively.…”

“…The increased depth implies extensive flooding of terrestrial vegetation and could relate to production of prey resources for larvae (Quist et al, 2004). However, the plateau shape of relationships between water level and species richness as well as abundance indicated that the larval fish preferred the shallow littoral area rather than the deeper zone (Brosse et al, 2007).…”