Spatial distribution of littoral fish species in a large European lake, Lake Constance, Germany

The spatial distribution and patterns of habitat use of littoral fish species in Lake Constance were studied using electric fishing and trammel net sampling to assess fish abundance and biomass in three depth strata at six different sampling sites within the littoral zone. Distribution differences among depth strata were found to be often more pronounced than among different sampling sites. Juvenile chub (Leuciscus cephalus) and dace (Leuciscus leuciscus) were most abundant in the shallow areas of <50 cm water depth with maxima of 54.9 and 29.2 ind. 100 m[-2]. Juvenile bream (Abramis brama) were collected mainly in the deeper littoral parts within areas of dense submerged aquatic vegetation with maximal abundances of 63.3 ind 100 m[-2]. Distribution of European eel (Anguilla anguilla) was found to be strongly dependent on the availability of adequate shelter. Dense accumulations of up to 61.7 ind and 40,000 g-wet. 100 m[-2] were recorded within single samples at a boulder site. The benthic burbot (Lota Iota) and stone loach (Noemacheilus barbatulus) also reached peak abundances in the shallow areas with up to 18.7 and 13.1 ind. 100 m[-2]. The distribution of both species was strongly correlated with the availability of gravel substrate and shelter provided by larger stones. All percid species were found mainly in deeper littoral areas. Juvenile perch and ruffe used areas of submerged aquatic vegetation as preferred habitat. Older individuals of both species seemed to avoid these areas and were caught in greater abundances and biomasses in open, unvegetated habitats. The study shows a remarkably high temporal and spatial diversity in the littoral fish species of Lake Constance compared to many small North American lake ecosystems. The results also clearly demonstrate the importance of sampling with high spatial resolution for studies of littoral fish communities. Especially in large lakes, depth and size separation of fish species within single sampling sites may be as important for littoral habitat partitioning as distribution differences among different sampling sites.