Quantifying littoral vertical habitat structure and fish community associations using underwater visual census

We developed and tested a new visual census technique to quantify the importance of vertical habitat structure on the associated fish assemblages in the littoral zone of a freshwater lake. We demonstrated that the primary environmental gradient, accounting for the most variation in the species data, represented a temporal gradient of seasonal characteristics. The secondary environmental gradient was related to the vertical structure at the sampling locations, showing the importance of the vertical component of the environment on fish community structure. Characterizing the vertical component at different resolutions provided different interpretations. The primary difference was the strength of influence of woody material on community structure. Woody material had a stronger influence on community structure throughout the water column when a single vertical unit defined the fish data. The appropriateness of defining the data by either multiple vertical strata or by a single vertical one would be dependent on the objectives of the study, as neither approach was found to explain substantially more variation in the species data. The current study demonstrates that fish are closely associated with particular elements of habitat structure in the littoral zone, even in the absence of major piscivorous predators. We provide a novel study quantifying the vertical multiple habitat structures and habitat use by fish in the water column of a freshwater lake. The new vertical visual census technique can be used to more comprehensively sample the three-dimensional environment of lake littoral zones, and quantify the fish-habitat spatial relationships across a range of abiotic and biotic habitat features.