Linking fluvial fish community to physical habitat in large woody debris: sampling effort, accuracy and precision

Large Woody Debris (LWD) in running waters provides complex and important h abitat for fish communities. Quantifying the structure of LWD should improv e the understanding of habitat choice of fish as well as fish habitat manag ement. Therefore, we evaluated the efficiency of techniques to describe phy sical habitat and fluvial fish community characteristics that are required to quantify fish-habitat relationships for LWD. An open electrofishing tech nique for 15 minutes with two electrodes captured more than 70 % of the fis h through a single removal in a 50 m(2) zone. On average only 3.4 % of the fish escaped from the zone during electrofishing. Mean conditions and varia bility of physical LWD habitat in a sampled zone could be accurately and pr ecisely described with 10 (water depth, current velocity, mineral bottom su bstrate size) or 20 (LWD variables) point measurements. Partial Least Squar e (PLS) regressions showed the potential of the LWD sampling procedure to r elate fish community characteristics to physical habitat. Fish abundance wa s significantly related to current velocity, water depth and mineral substr ate size, which are traditionally used in studies of fish-habitat relations hips. In addition, depending on the species, abundances were significantly related to various LWD variables that characterised density, location, shel ter function and structural diversity of LWD.