The survey on the fishery resources and environmental conditions in the Natori River estuary

Representative Organization: Tohoku University

2015/04/01 - 2016/03/31
Monthly

the Natori River estuary in Miyagi Prefecture

Field survey

Surveys have been proceeding to clear the status of fishery resources and environmental conditions in the Natori River Estuary and support the reconstruction of fishery. 1. Monitoring of the physical environmental conditions (Water Depth, Water temperature,Salinity). 2.The survey on the Manila clam population status(Population density, Size distribution) 3.The survey on the Blackish-water clam population status(Population density, Size distribution) 4. the Survey on the Ayu population status.

(1) Brackish water clam (Corbicula japonica) Brackish water clam abundance has returned to approximately the same levels as before the tsunami, but with an upstream shift in the C. japonica habitat of about 1 km due to movement of the brackish water zone. High abundance of the clam during 3 years (2013-2015) contributed the recovery of Hirose Natori River Fisherman Cooperative. (2) Ayu (Plecoglossus altivelis altivelis) The CPUE of ayu in 2011 is the lowest in past years. The residual upstream ayu population seems to have grown successfully and reproduced despite the effects of the tsunami, one year after the tsunami occurred, the ayu population had recovered to the same level as before the event. The research in 2012-2015 denoted large amount of ayu population running up. Especially, leisure fishing has been progressing in upper stream. (3) Manila clam (Ruditapes philippinarum) Manila clam recruitment has not yet occurred successfully since the tsunami. In 2015, the research indicated no mass reduction of the Manila clam, and spring-spawned juveniles grew normally from May to August. The data logger recorded normal range in salinity fluctuating on tidal rhythms. It is suggested the steady inflow of seawater is affecting the habitat condition of the Manila clam. From June 2015, the Japanese Ministry of Land, Infrastructure, Transport and Tourism will remove the sand spit to try to enhance recovery of environmental conditions in the Natori River estuary. In addition, these physical environmental changes induced the high abundance of another clam species, Nuttalia olovacea, and the distribution of some marine bivalves in the estuary. However heavy rain and huge discharges caused the large impact to the estuary in September 2015. The survey in November indicated reduction of population density of bivalves. It is important to monitor population status of the clam and environmental conditions.

FY2015 The survey on the fishery resources and environmental conditions in the Natori River estuary

Water temperature and salinity in the Natori River Estuary (FY2015)
Distribution of bivalves in the Natori River Estuary in 2015
Water temperature and salinity in the Natori River Estuary (FY2015-2016)