Influence of habitat, gear configuration and sampler characteristics on assessments of fish communities in inland waters

Accurate fish community assessment is of vital importance to freshwater resource management. This study aims to identify biases in survey methods used to describe fish communities with special emphasis on electro fishing and angling in the littoral zone of two freshwater systems located in northwestern Germany: lake Müggelsee and the river Spree. Distinct littoral habitats of lakes are known to harbor unique fish communities. Not for all of these habitats the associated fish communities have been investigated. Fishes were caught to characterize different habitats based on species composition, fish diversity, fish density, mean length, biomass per unit effort (BPUE) and condition. Submerged macrophyte beds, reed belts and unstructured sand, were sampled by point-abundance electrofishing and species composition, diversity and density differed among the habitat types. Reed belts showed higher species and fish densities than submerged macrophytes and sand. Findings thus indicate that fish assemblages differ based on the habitat. Every sampling gear available to assess fish assemblages has its own biases. To find differences in sampling efficiency, catch per unit effort (CPUE), BPUE, length and fish diversity were compared for 2 types of electrofishing gear: an 8KW anodic hand net and a 13KW strip anode. The two gear types differed when comparing fish diversity, and length frequencies and thus are suggested to produce different outcomes in fish community assessments. To identify whether sampler characteristics and angling gear had an effect on the catch outcome anglers of different experience levels varied hook size, bait size, bait type and the amount of ground bait. Expert anglers showed to be more efficient in terms of catch rate while inexperienced anglers incurred more bleeding fish. Bait size had no impact on catch outcome while the use of ground bait increases the catch rates. The results suggest that sampler characteristic and gear affect the outcome of angling-based surveys. In total the results of this study can be valuable directives for future studies on which parameters to consider when assessing fish communities. This advancement in the scientific methodology will help to increase the accuracy of fish assessments and ultimately facilitate the preservation of fish communities through more effective management.