1Yamanashi Prefectural Fisheries Technology Center, Kai, Yamanashi 400-0121, 2Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, 3National Research Institute of Aquaculture, Fisheries Research Agency, Ueda, Nagano 386-0031, Japan
We investigated factors preventing the establishment of stocked ayu Plecoglossus altivelis by sampling with casting nets and measuring microhabitat at several locations. In our analysis, three factors were selected as explanatory variables of the probability of capture of more than one ayu (or not) per casting net: 1) larger diameter of drifted sands, 2) lower frequency of cobbles (size class of 65-256 mm) and boulders (>256 mm), and 3) higher frequency of cobbles and boulders buried by sands or caddisfly cases. These three factors were strongly correlated with the amount of drifted sands. We concluded that the amount of drifted sands is useful as an indicator for management decisions concerning stocking sites.