Fishery catches of kuruma prawn Penaeus japonicus have declined since the mid-1990s despite substantial efforts to enhance the stock by reseeding programs in Japan. To investigate the status of new settlement, postlarvae and juveniles of the prawn were collected using rake sledge nets on the tidal flats in Ise Bay, Mikawa Bay, and Lake Hamana on the Pacific coast of central Japan. During the study period from summer to winter in 2018, 2019, and 2020, settlement of natural postlarvae was observed despite extremely low stock levels of the adults. The peak of the settlement occurred from late summer to autumn although it used to generally occur in early summer in years with a high stock level. The body size of the prawn captured by fisheries is known to be smaller in years with a low stock level than in years with a high stock level. A possible reason for the delayed settlement is thought to be related to the decrease in the number of larger individuals which are known to spawn earlier than smaller ones.

　In this study, a small-sized macroalgal bed was restored through the removal of sea urchins at a barren site in Kashiyama, Nagasaki Prefecture. Sea urchin densities decreased from 13.9 to 0.7 individuals/m² from June to November 2015, and remained low afterward. By the following spring, small-sized macroalgae such as Gelidiaceae spp. and Chondrophycus undulatus increased while large-sized macroalgae did not. The coverage of the small-sized macroalgae was three times that of the control area, in which the densities of sea urchins exceeded 12.2 individuals/m² throughout the experimental period. Tank experiments showed that many of the small-sized macroalgae examined (Dictyopteris undulata, D. prolifera, Gelidium elegans, and Dichotomaria falcata) were less vulnerable to feeding by Siganus fuscescens and Kyphosus bigibbus than large-sized macroalgae (Sargassum alternato-pinnatum). Our results indicate that small-sized macroalgal beds can be more easily restored than large-sized macroalgal beds simply through the removal of sea urchins, even under high browsing pressure from herbivorous fish. In small-sized macroalgal beds, the gonad index of Heliocidaris crassispina was higher than that of animals in the barren areas. Therefore, the restoration of small-sized macroalgal beds would likely be advantageous to sea urchin fisheries.

　The fatty acid composition of sakura shrimp muscle was used to determine the origin and estimate the dietary habits of the shrimp. The major fatty acids in sakura shrimp muscle were C16:0, C18:1n-9, C20:5n-3, and C22:6n-3. The discrimination rate between sakura shrimp from Suruga Bay and Taiwan was 90%. Consequently, it is considered possible to distinguish between shrimp from these locations based on the fatty acid composition. In addition, a positive correlation was found between the body weight and C18:1n-9/C18:1n-7 ratio of sakura shrimp from both Suruga Bay and Taiwan. Therefore, it is suggested that sakura shrimp may change their diet from herbivorous to carnivorous as they grow.

　This study evaluated the manufacturing process of surimi, involving recycling of fish flesh-soaking water after removing lipids and proteins from wastewater. Even after the soaking water was used five times, the lipid, protein, and iron contents in the soaked flesh were significantly lower than before soaking. Therefore, recycling the soaking water did not reduce the effects of water soaking. Of the protein content effused in the wastewater, 57-70% was recovered as heat-coagulated products, reducing the total volume of wastewater to a fifth. Therefore, the loading of the wastewater was greatly reduced. If heat-coagulated products can be converted into food ingredients and reused soaking water extracts can be recycled as raw materials, it may become possible to manufacture surimi without producing any waste materials.

　One way to expand online seafood sales is to extract information about products and services from online posts left by consumers and use it as a hint for improving products and services. However, there has not been enough research on collecting many online posts about seafood sales services and extracting information efficienstly. The purpose of this paper was to analyze online consumers' opinions about seafood sales services using a topic model and to obtain suggestions that will lead to the use of online sales of seafood by more consumers. The data were collected from three online services related to S, a seafood sales service that operates multiple stores and e-commerce sites in Tokyo. First, morphological analysis was conducted on all the data. Then, a set number of topics were extracted using Gensim, a library of Python, and assigned meanings. As a result, it was suggested that to encourage more consumers to use online seafood sales services free from anxiety and mistrust, it is important to adjust expectations for the quality of marine foods so that they do not deviate too much from the actual situation.