2012 Volume 15 Issue 2 Pages 147-160
We examined use of small perennial agricultural canals by fish according to seasons and life stages and habitat characteristics in 4 regions, southern Gifu, central Japan, in irrigation (June and August) and non-irrigation (September and February) periods. Seasonal changes in the number and size composition of six dominant fish species showed that the canals function as habitat for growing and overwintering. Total abundance of all fish species was higher in earth canals, which had natural bed materials, than in concrete canals in all study periods other than August. Fish diversity was higher in earth canals than in concrete canals only in winter (February) . Abundance of each of most dominant fish species was positively related to the bed materials, such as silt, sand, or gravel, in warmer seasons (from June to September) . In winter, that was primarily explained by cover ratio or water depth. In addition, we found close positive relationship between bitterling and mussel abundance in three study periods including spawning and other seasons. These habitat characteristics according to the study periods were satisfied in earth canals. Our findings suggest that a set of natural bed materials and covers, such as bank vegetation and undercut bank, is important when canals are considered as fish habitat throughout irrigation and nonirrigation periods including winter. Therefore, the bank-lined canal with natural bed should be adopted for canal construction and modification, although unlined earth canal is ideal. If the canal bed is necessarily lined, the hydrological conditions that allow sediment deposition should be ensured.
