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

Abstract

Large Woody Debris (LWD) in running waters provides complex and important habitat for fish communities. Quantifying the structure of LWD should improve the understanding of habitat choice of fish as well as fish habitat management. Therefore, we evaluated the efficiency of techniques to describe physical habitat and fluvial fish community characteristics that are required to quantify fish-habitat relationships for LWD. An open electrofishing technique for 15 minutes with two electrodes captured more than 70 % of the fish 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 variability of physical LWD habitat in a sampled zone could be accurately and precisely described with 10 (water depth, current velocity, mineral bottom substrate size) or 20 (LWD variables) point measurements. Partial Least Square (PLS) regressions showed the potential of the LWD sampling procedure to relate fish community characteristics to physical habitat. Fish abundance was significantly related to current velocity, water depth and mineral substrate size, which are traditionally used in studies of fish-habitat relationships. In addition, depending on the species, abundances were significantly related to various LWD variables that characterised density, location, shelter function and structural diversity of LWD.