An offshore trawl fishery within Shimane Prefecture in Japan has introduced mobile protected areas using information from fisheries to manage the resources of the small blackthroat seaperch Doederleinia berycoides since 2012. However, there is an increasing need to understand the distribution of these fish within the entire sea area in advance and to set up efficient protected areas using this information. In this study, we used a random forest method to develop a model for predicting the distribution of these fish in the southwestern Japan Sea using the operating information of the offshore trawl fishery from March to May of 2011–2018 and estimated values of bottom water temperature, salinity, and tidal current. The prediction error against out-of-bag (OOB) data for a model developed in the year of operation was 14.5% and that developed using CPUE in the first half of the fishing year was 14.6%. In addition, the prediction accuracy for test operations by a research vessel was 94%. Based on these results, we elucidated the spatiotemporal distribution of this fish and discussed the characteristics of factors affecting the distribution.

The homing migration and catch amount of chum salmon (Oncorhynchus keta) depend on the physical conditions of the coastal water in the autumn, which are likely to change due to the recent warming trend. We analyzed catch numbers at four salmon set nets placed 1.9–14.1 km southwest off the mouth of Ishikari River. We also analyzed water temperature observed at two of the nets in September and October 2017. Between October 4–6 and 16–18, we observed the highest catches, each of which corresponded to a minimum water temperature and a maximum downward vertical gradient. Each event followed the occurrence of a maximum water level at the mouth of the river with a time lag of 6–7 days, indicating that a freshwater plume from the Ishikari River possibly attracted more salmon. A heat and volume conservation model, which was applied to the estimated amount of the river discharge, resulted in the plume increasing to 37 km in radius covering the inner part of Ishikari Bay where the set nets existed. We estimated the dilution of the river water to be 11.3% due to the extension of the plume, which was 1–2 orders of magnitude larger than the lower limit of concentration at which salmonoids can distinguish their original river water, suggesting salmon off the coast were attracted to the plume and caught. As the salmon catch increased earlier at the set nets that were situated further away from the river mouth, they may have concentrated southwest of the mouth. We also discuss the importance of seasonality in oceanic conditions on the west coast of Hokkaido to the returning of salmon.

To understand the fisheries biology of rabbitfish Siganus fuscescens in the eastern Seto Inland Sea, Japan, we examined the age, growth, and spawning period of fish collected off Okayama, Kagawa, and Tokushima Prefectures from April to December, 2013. The standard length ranged from 117 to 310 mm. The gonadosomatic index (GSI) which ranged from 0.04 to 40.36 in females and from 0.01 to 30.16 in males, was high from the middle of June to the end of July and low in the other months. Based on histological observation of gonads in June and July, the females with GSI of ≥3.57 and males with GSI of ≥4.79 matured, and females with involution stage were observed in late July. The females with GSI of ≥3.57 and males with GSI of ≥4.79 appeared from June to August and from June to July, respectively. The GSI of both sexes was high from the middle of June to the end of July. These findings suggest that the fish spawned from June to August and the main spawning season was from between the middle of June to the end of July. The check mark on otoliths was formed once a year from June to August. The maximum ages for males and females were 4 and 8 years old, respectively. There was no significant growth difference between males and females. The von Bertalanffy growth equation estimated as follows: SL_t=255 (1−e^{−0.56(t+0.95)}), for where SL_t is the standard length (mm) at age t (year). The relationship between standard length (mm) and body weight (g) was expressed as follows: BW=2.87・10⁻⁵・SL ^3.00.

Most studies on the effects of artificial reefs (AR) have used fishery-independent research data, and very few have utilized actual commercial fisheries data sets (fishery-dependent data). Commercial fisheries catches and nominal catch per unit effort (CPUE), which is calculated by dividing catch by effort, are considerably impacted by many factors, including the AR effect, the fishing area, the ship’s capacity, and annual and seasonal resource fluctuations. If nominal CPUE data are used for analysis, the independent effects of an AR on resources density cannot be accurately estimated. To overcome the above difficulties, we applied standardized CPUE methods and estimated the spatial range of AR effects for three species (Hyperoglyphe japonica, Seriola lalandi, and Parapristipoma trilineatum). For H. japonica, the resource density near ARs was seven times higher than that in natural reef areas, with effects ranging up to <350 m from the AR center. For S. lalandi, typical effects ranged up to <100 m from the AR center; however, the effect of AR on P. trilineatum was limited to the immediate AR area.