The scale of eel stocking/restocking in Japan has reached a level comparable to that of the domestic annual catch, however, there is limited knowledge regarding the effectiveness and impact of eel stocking/restocking, highlighting the need for further research and investigation. With the aim of contributing to the development of future research on Japanese eel stocking/restocking, we have compiled existing knowledge on the stocking/restocking of Anguillid eel species worldwide. Currently, it is not possible to determine whether eel stocking/restocking contributes to resource recovery through reproduction. While potential effects such as temporarily maintaining and increasing fishery resources and preserving and restoring biodiversity are anticipated, negative impacts such as intensified intra-species competition and the spread of pathogens are also expected.
Field surveys were conducted to assess annual production of meiobenthos at 57 stations in the Seto Inland Sea from 2011 to 2014. The annual mean density of meiobenthos was 400–1,000 ind./10 cm2 at most stations in the Seto Inland Sea, and it was considered that seasonal fluctuations of meiobenthos density were high from spring to summer and decreased from autumn to winter in many areas of the sea. The density of nematodes was highest at most stations, but the biomass of copepods exceeded that of nematodes at many stations. The density of benthic copepods tended to be higher in shallow water areas where the amount of organic matter in the bottom sediment was high, and the production of benthic copepods exceeded that of nematodes. In the sea area (average depth 48 m) where the mud content and the amount of organic matter were low, the production of meiobenthos was low, but the production by polychaetes was high.
Since 2016, the catch of Japanese common squid Todarodes pacificus has been poor and squid processing companies have faced shortages of squid ingredients. In this study, we examined the situation of squid processing companies and their countermeasures by compiling statistical data and conducting interview surveys. The results showed that squid processing companies have used various imported and domestic squid to compensate for the shortages according to their processing levels and product types. Based on these findings, we considered measures to reliably secure squid ingredients and to develop and utilize domestic squid other than Japanese common squid.