| The microhabitat characteristics of the Tokyo bitterling, Tanakia tanago, designated a natural monument of Japan, were investigated in its natural habitat. To elucidate the habitat requirements of juvenile bitterling, we analyzed the relationships between the occurrence (presence/absence) of juveniles and microhabitat variables using a generalized linear mixed model (GLMM). The model showed that the occurrence of juveniles was positively correlated with the presence of underwater cover and the number of bitterling eggs deposited in adjacent mussels, and negatively correlated with current velocity. When the habitat was evaluated using this model, it predicted that the occurrence probability of juveniles was low in the upper reach of the canal. Therefore, the upper reach habitat was restored (i.e., the bottom was excavated, stakes were installed, and mussels were introduced) after considering the habitat requirements of juveniles. To assess the effect of these restorations, we compared the occurrence of juveniles between restored and control (non-restored) stations. Over the duration of the observations, 99 and 41 juveniles were found at restored and control stations, respectively; 71％ of the total number of juveniles was observed in the restored sections. These results suggest that the restoration scheme could increase suitable habitat for juvenile bitterling. Assuming that the juveniles observed in the upper reach of the canal survive and breed, the size of this population should increase. The habitat-requirement model constructed in this study should be applicable for maintenance and reconstruction of habitats of this species. |
