The Honjo area was surrounded by dikes for reclamation work and separated from Lake Nakaumi in 1981. However, the work was frozen and the area still remains as a closed water area. Tidal flow pipes were constructed for the evaluation of fishery promotion between Honjo area and Hokubushosuiro channel in March 1998.
The benthic fauna of Honjo area was surveyed during April 1997 to march 1999 at 6 sites in the area and 1 site in Seibushosuiro.
In order to evaluate the effect of tidal flow pipes, the benthic fauna data before and after was compared. No change was observed except near the pipes. But, conspicuous change observed near the pipes. Musculus senhousia increased at St.1, 2 near the pipes after constructed . And number of spices increased, too in nearest station. Similarity Index between St.6 and St.1, 2 near the pipes was higher after constructed.