Research on Fishery resources and environmental condition on fishery ground in the Natori River

Representative Organization: Tohoku University

2013/04/01 - 2014/03/31
Once a month

Natori River

Field survey

1. The population density of the short necked clam (Ruditapes philippinarum) and environmental conditions. The short necked clams were collected using pumping system in Natori River. Population density of the clam was calculated and shell size compositions were analyzed. Surveys on the environmental conditions were analyzed. 2. The population density of the clam (Corbicula japonica) and environmental conditions in Natori River. 3. Growth experiment of the bivalve (Corbicula japonica) using caging method in Natori River. The growth and production level were evaluated. 4.The condition of the Ayu (Plecoglossus altivelis ) population in the Natori River and Hirose River. Fish were collecting using casting net at three stations. CPUEs and hatching date compositions and GSI were compared with previous ones.

1. Distribution of the clams and environmental conditions Density of short necked clam (Ruditapes philippinarum) was higher in sandy bottom area located near river mouth stations. Density of the short necked clams in the silty bottom was low. Individual numbers of short necked clam was around 500 ind./m2 in June and July. Shell length of the clam was about 10mm or shorter. Many of them were juveniles of the clam. That indicates that the clams could reproduce and their larvae could settled the bottom and they have been growing. However, in September, many of the clams, short necked clam have been disappeared.Individual of numbers is near zero in all stations. The reason of decrease in population density of the clam is considered lower salinity for long period caused by rain fall in summer and autumn. Main problem is unstable environmental conditions for short necked clam and we should resolve the mechanisms of the reasons causing lower salinity. 2. Corbicula japonica population and environmental conditions Population density of Corbicula japonica was high level in Aug. 2014 and it suggests recover of Corbicula japonica resource as the same level before the great earthquake. Shifting habitat of these is attributed to extending of the brackish area about1km upstream. At the station near the river mouth, rising salinity depressed the density if the clam Corbicula japonica remaerkably. (continued to Remarks)

FY2013 Research on Fishery resources and environmental condition on fishery ground in the Natori River

Water temperature and salinity in the Natori River Estuary (FY2013)
Distribution of bivalves in the Natori River Estuary in 2013
Distribution of bivalves in the Natori River Estuary in 2014