Distribution of the oriental weatherloach, Misgurnus anguillicaudatus, in paddy fields and its implications for conservation in Sado Island, Japan

The distribution of the oriental weatherloach, Misgurnus anguillicaudatus, together with related environmental factors were surveyed at 185 paddy field locations on Sado Island in Japan. This was associated with the reintroduction of the Japanese crested ibis, Nipponia nippon, which prefers to feed on the loach. Loach were found to be present at 90 locations (49%). Analysis with GIS, GLM and AIC revealed that positive factors for the loach distribution included the presence of an earth ditch, the connections at outlets and the proportion of paddy field area within an 800 m radius. Conversely, pumping-up water irrigation and flow irrigation affected loach distribution negatively. In an interview survey that was conducted concurrently, older farmers in the area recalled that the loach had once been distributed over almost the entire island (89/96, 93%) about half a century ago. The farmers also suggested that the impact of agricultural chemicals was one of the main reasons for loach reduction or local extinction. A map of the current potential loach distribution was made using the best fit model from GIS variables. The loach was expected to be distributed in the Kuninaka region with high probability (60–100%) and in patches in the Osado and Kosado regions with low–medium probability (10–50%). As a feasible scenario for the conservation of the loach, another predictive map of the loach distributions was made using a model fit based on the GIS variables and outlet connection, in which the all of the outlets were presumed to be connected to the ditches without gaps. In this case, the loach were expected to be distributed almost throughout the paddy fields with medium–high probability (40–100%). In another scenario that presumed the complete land consolidation of all the paddy fields, the probability of loach occurrence was low (0–30%) throughout the island with the exception of the island’s center in the Kuninaka region.