Natural and anthropogenic factors influencing fishes in the littoral zone of alpine and pre-alpine lakes
Studying aquatic biodiversity in nature allows us to better understand, manage and protect it against increasing human stressors. In this study, I investigated factors shaping the littoral fish communities of lakes in and around the Alps. The nation-wide sampling program, “Projet Lac” sampled 27 lakes located mainly in Switzerland (but also in France, Germany, Austria and Italy) with standardised fish sampling methods (electrofishing, vertical and CEN gillnets) and documented 48 littoral fish species.
I analysed the data from Projet Lac to identify the littoral habitats to which each fish species was positively (“attracted to”) or negatively (“avoiding”) associated. I further identified the lake-scale factors that explained variation in species-habitat associations among lakes. I next determined the environmental factors explaining spatial variation in littoral fishes within each lake and among all lakes. Within lakes, I considered bathymetric slope, distance to river inflow, wave exposure, adjacent land use, as well as habitat type, composition and physical complexity. Among lakes, I tested the influence on average littoral fish catches of variation in lake productivity, morphology, altitude, and habitat composition.
I found significant associations between fish species occurrence and habitats for many species, the strongest being a positive association of perch with boulder habitat, which was consistent among lakes. Habitat associations differed among species, but also within species among lakes and between morphs of the same species within a lake. For example, habitat associations differed between perch colour morphs in Lake Geneva. Ontogeny also influenced habitat association, with smaller individuals associating with more structurally complex habitats. Lake phosphorus concentration had strong effects on fish abundance, biomass and habitat associations among lakes. Bathymetric slope influenced multiple aspects of the fish community within lakes. For example, the probability of catching a fish of any species by electrofishing was higher in steeper littoral areas. Wave exposure was also important in shaping the fish community of Lake Geneva, with four fish species more common in exposed sites and two species preferring more sheltered areas.
Understanding how fish species are differentially distributed among littoral habitats can provide information for preserving fish diversity and maintaining ecosystem function. In particular, knowledge of fish habitat associations can be useful for lake management by guiding planning and success evaluation of lakeshore restorations. While general ecological patterns can be useful to guide lake management in the absence of other information, idiosyncratic results such as the importance of wave exposure in shaping the fish community of Lake Geneva, particularly highlight the importance of considering local conditions and key drivers within each lake