Assessment of a unionid freshwater mussel (Pronodularia japanensis) population in an agricultural channel during the 4 years following reintroduction

Abstract

Detailed procedures for the reintroduction of endangered freshwater mussel species (order Unionoida) after habitat modification, and the population-level consequences of this, have not been reported for agricultural channels. We reintroduced Pronodularia japanensis (Lea, 1859) into a 70-m-long channel after a concrete lining had been inserted. The habitat quality was improved by providing a channel bed with gravel-sand substrate. Four years of monitoring following the reintroduction (3.5 years over four growing and reproductive seasons) showed the continuous recruitment of juvenile P. japanensis to a total of 79 individuals, but a decrease in the number of reintroduced individuals 440 to 118. The population size reached a relatively stable in the first 0.7 years, but remained approximately half the original size for the rest of the monitoring period, despite continuous recruitment. Our findings suggest that the reintroduction of freshwater mussels with appropriate treatment of their habitat helps to maintain the reproduction of local populations for at least 4 years.