Inhabiting Situation of the Asian Clam (Corbicula fluminea) in the No.1 Main Channel of Miyagawa Irrigation Network

Abstract

The terminal pipelines of the Miyagawa Irrigation Network in Mie prefecture are increasingly being clogged due to the accumulation of Asian clams. To counteract this clogging, the Miyagawa Land Improvement District conducts sludge discharge operations at 35 points along the pipeline. In this study, we examined the transport of Asian clams using sludge discharge data from Myojo Sludge Discharge Point No.1, located on Main Channel No. 1. Asian clams were dislodged during times of high water velocity, such as during the rice planting season and the period after the mid-summer drainage. In addition, our survey of pipelines with an inner diameter of 2,000 mm suggests that Asian clams inhabit sediments that accumulate in the notch that occurs where a pipe joins a pipe fitting. According to our study of Asian clams collected in such notches during in-pipe surveys in December 2016, more than 90% of the Asian clams occurred in high-density aggregations of approximately 6,000 individuals m^-2. In addition, our numerical calculations of bed load transport indicate that there is a high probability that Asian clams with a shell length of 20 mm or greater may inhabit a pipe fitting for multiple years.