| Most freshwater shrimps in Japan are amphidromous species. We have recently observed that large numbers of amphidromous shrimps migrated into agricultural drainage channels of our research site. However、 these shrimps could not survive in a channel since they dried up during the non-irrigation period (Nakata et al.、 submitted). To effectively conserve migrating shrimp populations、 we have tried to clarify the habitat utilization patterns of the shrimps in relation to the irrigation system. In this study、 we conducted a series of field surveys in eight channels during the irrigation period (June to September) and non-irrigation period (October to May)、 to clarify the shrimp distribution and the environmental factors affecting the channels. No shrimps were captured in all channels in July、 but two amphidromous shrimp species (mostly Caridina leucosticta) were collected in seven channels in September. In October、 water from the fields had disappeared in all channels. Four channels、 including one spring-fed channel、 had almost dried up by November and the shrimps that had migrated there were considered not to be able to survive. In contrast、 many shrimps had migrated into two spring-fed channels until November because spring water provided a stable and suitable environment for shrimps. Only a few non-diadromous shrimps were observed in our surveys、 which indicate that they could not reproduce in the channels of our research site. These results indicate that fluctuations in the water supply、 which is determined by the irrigation system、 affected the shrimp species composition in the channels. |
