| Drainage (irrigation) channels for agriculture potentially function as habitat for fish originally depending on broad、 lowland floodplains. Non-irrigation period is critical for fish survival or persistence in the drainage channel because of the severity due to low flow discharge caused by closing the water gates and low water temperature during the period. To examine factors affecting fish assemblage in the drainage channels during non-irrigation period、 we conducted fish sampling and measurement of physical environments (depth、 current velocity、 bed material、 and area of vegetation cover) in 13 drainage channels (ranging from 6 to 16 m in channel length)、 Seki-city、 central Japan、 during autumn (September) and winter (February). Fish were captured using dip nets and D-shaped nets. In autumn immediately after the reduction of flow discharge in the drainage channels、 fish abundance was negatively related to the proportion of concrete in bed materials、 while fish diversity was positively related to that of gravel-pebble. In winter、 fish abundance and diversity were positively related to the area of vegetation (grasses) covers and water depth、 respectively. These results indicate that perennial flow and grasses along channel margins are important components of winter habitat for fish assemblage in the drainage channels and that the alteration of channel bed from natural bed materials such as gravel and pebble to concrete results in degradation of fish assemblage. In addition、 throughout the study period (autumn to winter)、 minimum of mean water depth in the two study periods explained low abundance and low species richness of fish in the drainage channels. Our study suggests that flow discharge、 sediment、 and vegetation should be maintained to conserve fish assemblages in the drainage channels. |
