環境

The SCOP100 survey (May of 2014 and 2015), the spiny goby fishing survey (September and December of 2014), and the mudskipper population survey (October of 2014 and 2015) were implemented as a continuation of citizens' environmental studies implemented before this research or at some point in the past. In addition, a comparative survey of river use status for the Edo River flood channels and the Tama River estuary through observation and interviews (total of 12 times between May and December 2014), analysis of indirect information such as fishing magazines and fishing lodgings, and questionnaires and current status surveys on waterfront “fun schools” (2015), were implemented as development surveys.

The 2014 SCOP100 survey confirmed that although the regular species for an average year were confirmed, the freshwater clam population continued to decline over time. Also, as a reduction in the area of tidal flats in the targeted sites, an increase in reeds, and an increase in ground height were confirmed. In particular, the latter phenomenon has been suggested as the cause of the mudskipper population decline in the targeted sites by comparing with past citizen survey results. The 2015 SCOP100 survey was the first survey carried out after moving upstream of the Kawasaki Daishi Bridge, following a change in the sponsoring organization brought about for the purpose of continuation of the study.

The left bank of the Tama River estuary that had seawall improvements continues to be used as a shore fishing site for goby although they are not found in the abundance seen in the Edo River flood channels, and it attracts complaints of littering and other problems. The results of the ship fishing survey showed a smaller catch in December than in September, thus suggesting that the season for harvesting the population from the first spawning season was over. In addition, the possibility of the presence of a spawning group in the Tama River estuary was indicated by integrating previous findings and past fry surveys.

We have been proactively involved in the Tama River estuary through past research sponsored by the Foundation and participation in the Haneda collaborative research. All survey results confirm transformations in the location, unique environmental characteristics, distribution of wildlife, and other issues; and we continue to recognize the importance of monitoring these on an ongoing basis. In particular, the SCOP100 survey will be continued primarily by a local NPO, and their second survey is to be carried out in May 2016.

With the existence of key persons and key stations such as the Daishigawara Flats Museum, past parties have become collaborators and everything have started anew, inheriting the past documents and research networks. However, on the Tama River estuary, where no spiny goby pleasure boats are present, the watchful eyes of regional fishermen who are said to be strong enthusiasts are important and we hope to share information with them.

Satoru Suzuki、Association for Shore Environment Creation
Takashi Kimura、Association for Shore Environment Creation
Society and Environment Laboratory、 Chiba Institute of Technology