Support and reconstruction of fishery in the estuary and coastal area

Representative Organization: Tohoku University

2019/04/01 - 2020/03/31
Every month

Natori River Estuary, Sendai Bay, Ishinomaki Bay

Field survey

1.Survey on the environmental conditions of fishery ground of bivalves Research the change in physical environment and bivalve distributions. To clarify the connection between physical environment and the quantity of the Manila clam. Estimation the effect of salinity on the Manila clam using EFDC (Environmental Fluid Dynamics Code) Model. Discussion on an approach for the restoration of the Manila clam fishery. 2. Survey on the resources of the bivalves Survey on the distribution of bivalves, Brackish water clam , the Manila clam and Nuttallia olivacea. Research on the growth and survival rate of the Manila clam in some stations using caging experiments. Analyses of food utilization by the bivalves using carbon and nitrogen stable isotope ratios. 3. Survey on the ayu population Survey on the catch per unit effort of ayu population in the Natori River and Hirose River. Analysis of hatching date composition and body length composition of ayu. Comparison of growth rate of ayu between the Hirose River and the Natori River. Analysis of carbon and nitrogen stable isotope ratios of ayu, and microalgae in the river. 4. Estimation of the present stock of the Surf clam Research on the stock of the surf clam and body size distributions. Analysis of growth curve of the surf clam in this ground. Research on environmental conditions of fishery ground. Analysis of essential amino acids of the surf clam. 5. Analyses of the ark shell fishery and Simulation of fisheries management Research on the stock of the ark shell and body size distributions. Analyses of CPUE fluctuations of the ark shell using daily records of landing. Analysis of shell structure and growth pattern using oxygen isotope ratio.

1. Survey on the environmental conditions of fishery ground of bivalves EFDC (Environmental Fluid Dynamics Code) Model simulated the pattern of fluctuation on salinity in bottom water, and estimated relation between population density of the Manila clam and salinity conditions. The model suggested that lower than 15 PSU in salinity may induce decrease of the Manila clam. In 2019, low salinity didn't last than ever before due to the river-mouth widening. Restoration of the river mouth induced regular tidal flow. 2. Survey on the resources of the bivalves The higher population density of Brackish water clam recorded than before. Field experiment results showed that environments were better conditions for the Manila clam. However successful recruitment of the Manila clam has not yet occurred. Closing of the mouth of Idoura Inlet have been affecting decrease of capacity of seawater within the estuary. 3. Survey on the ayu population In 2019 the catch per unit effort of ayu population showed the same level as before the tsunami. Ayu in the Hirose River was estimated to hatch earlier than the Natori River. Growth rate of ayu in the Hirose River between June and July was higher than the Natori River. Nitrogen stable isotope ratios of ayu and micro algae in the Hirose River were significantly higher than the Natori River. Larger ayu tended to have a higher carbon stable isotope ratio in both rivers. 4. Estimation of the present stock of the Surf clam New fishing gears for the surf clam were bought out and we accelerated the technical transfer the fishermen. The present landing of the Surf clam achieved the same level before the tsunami. The 2014year class recruiting grew up to 400 to 500 tons in this year. The surf clam has so high essential amino acids, especially alanine, glutamic acids as important components on delicious taste, and it is good information for creating bland image. It is urgent for the fishery to construct a fishing system avoiding rubble. 5. Analyses of the ark shell fishery and Simulation of fisheries management The meeting and discussions have been conducted about strategy of sustainable management on ark shell. Released clams contribute to fisheries catch. Fishing effort less than 2500 and rotation of 2 years cycle make the ark shell catch sustainable with high level. Analysis using oxygen isotope ratio reveal that there is a time lag of constructed shell pattern between young and adult clam period. The shell captured in the offshore is worse than coast. It is necessary to understand growth differences for continuously controlled fisheries.

FY2019 Support and reconstruction of fishery in the estuary and coastal area

Distribution of manila clam