Seasonal habitat use of Hotoke loach, Lefua echigonia, inhabiting paddy fields with intercepting drains.

Abstract

A study was conducted to obtain basic information regarding conservation ofHotoke loach, Lefua echigonia, a fish species inhabiting paddy fields with intercepting drains on steep valleys or “yatsuda”. Two study sites （A and B） were characterized by different levels of movement barriers within the ditches and sections between the ditches and paddy field. The loach primarily inhabited the intercepting drains in both sites. In the site with fewer barriers （Site A）, the loach moved into the intercepting drains from ditches during January - June. Moreover, based on the finding that both adult and immature fish congregated in the intercepting drains, the loach was considered to use the intercepting drains for reproduction. In Site B, immature fish were also found largely in the intercepting drains, suggesting that this habitat was important for the juvenile fish. However, in the site with more barriers （Site B）, there were fewer indications of the loach moving into the intercepting drains in winter from the ditches and therefore, the intercepting drains were not utilized sufficiently for the overwintering or reproduction. In the habitat distribution model created by month and by fish age class, using population density as a dependent variable, monthly average water temperature, study site, water depth and underwater cover ration were selected as significant explanatory variables. In the habitat distribution model, monthly average water temperature negatively influenced the population in August but positively did so in January and June. This study suggests the intercepting drains with groundwater seepage function as habitats for reproduction, nurseries for immature loach, and overwintering. The intercepting drains would become even more effective habitats, if plant litter or submerged plants, in particular, exist and connectivity with the ditches is enhanced during January – June, and August – October periods when fish movement peaks.