Article ID: 2414
Abstract: The habitats of freshwater mussels (family Unionidae) have become fragmented and scattered in agricultural ditches due to changes in land use. Pronodularia cf. japanensis 1 is found in only three geographically distant agricultural ditches in Ehime. Farmland consolidation is scheduled, and rehabilitation of agricultural ditches is planned. All mussels must be collected during this process, temporarily reared elsewhere under different conditions, and then released post-consolidation. This study developed a method to relocate P. japanensis temporarily during farmland consolidation. We conducted an experiment with marked P. japanensis individuals reared in five indoor experimental tanks and two cages suspended in two irrigation ponds. Additionally, some marked individuals were released back into the original agricultural ditch. The survival and growth of all marked individuals were tracked. The survival rate of P. japanensis in the experimental tanks was approximately 60% over 7 months, regardless of whether they were fed cultured diatoms, water from a plankton-rich agricultural ditch or stream, or a mix of commercially available diatoms, haptophytes, a chlorophyte, and Nannochloropsis. No shell growth was observed during the indoor-rearing period. In contrast, the survival rate in one irrigation pond was 82% over 33 months, with an approximate increase in shell length of 1 mm. Shell length increased by about 2 mm over the same period in the original agricultural ditch. Thus, the pond strategy is superior. This system will be used to temporarily relocate endangered freshwater mussels during farmland consolidation. After rehabilitating the ditches, relocated individuals will be released, and their survival and growth will be monitored.
