The Japanese Society of Fisheries Science Award:

　　HIDEKI USHIO, REIJI MASUDA

The Japanese Society of Fisheries Science Award of Merit:

　　KEIICHI MUSHIAKE, YOH YAMASHITA

Scientific Achievement Award in Fisheries Science:

　　AKIRA INOUE, TETSUYA NISHIKAWA, SHO HOSOYA

Achievement Award for Young Scientist in Fisheries Science:

　　HIKARU ITAKURA, HIDEAKI MATSUI

Technical Achievement Award in Fisheries Science:

　　KAZUYOSHI KOMEYAMA, JUN-ICHI TSUBOI

　In this study, we evaluated the fuel consumption during towing of a modified trawl net and a conventional net in pair trawl fishery in the East China Sea. The modified trawl net was constructed using a combination of drag reduction techniques for bottom trawl nets, such as enlargement of the mesh size, reduction of the netting surface area, removal of the flapper, and use of a light ground rope. In total, 25 pairs of modified net and conventional net tows of fishing experiments were carried out. The fuel consumption while towing the modified net was reduced to 83.3–95.3% of that while towing the conventional net. No significant differences (p > 0.05) were observed in the amount and composition of the catch obtained with each net. The feasibility of energy-saving operations was confirmed by minimizing the impact on the catch, with improvement in the net drag reduction effect.

　We tested the use of a light trap to catch larval and juvenile non-native fish (largemouth bass, smallmouth bass, and bluegill) in lakes, reservoirs, and rivers at nine sites across four prefectures in Japan. A total of 18,409 individuals were captured in light traps lit with blue LEDs, with a trend towards capturing higher numbers of individuals in the early larval stages. The non-native fish were also captured in environments with a water clarity of <100 cm, confirming that light traps could be used to remove them even from muddy lakes. This method enabled the previously difficult capture of larval and juvenile non-native fish to be carried out effectively with little effort. However, it is necessary to consider the location and timing of installing traps to minimize bycatch.

　Parameters in the Ricker models of stock and recruitment of yellowtail Seriola quinqueradiata considering the effects of capturing juveniles were estimated using time series of number of recruits over 1994–2020, spawning stock biomass (SSB) and commercial catch number for juveniles under special permit for aquaculture. Equations expressing the relation between stock and recruitment are derived from the differential equation describing the density-dependent mortality process of juveniles with capture, and the catch equation for juveniles is derived using the equation. The unknown parameters are estimated by maximizing the log-likelihood with the above data. The estimations showed that the estimate of natural mortality coefficient averaged over 1994–1996 was 0.119 (per month), that over 2018–2020 was 0.310, and the estimate gradually increased. The annual estimate of fishing mortality coefficient for juveniles gradually decreased, whereas that of the natural coefficient rapidly increased. The current reduction of fishing coefficient restored the level of the expected number of recruits up to 90% of that without capture. Use of the model and its modification are discussed.

　With a view towards effective fisheries management, catch features, including catch per unit effort (CPUE; number of fish caught per angler per hour), sex ratio and maturity status of Honmoroko Gnathopogon caerulescens caught by recreational anglers using long dip nets in the Shinyamaji River inlet to Ibanaiko Lagoon, adjacent to Laka Biwa, were examined. Mature individuals caught from April to June 2020 and 2021 were characterized by the CPUE ranging from 10 to 50, and high gonadosomatic index, the sex ratio tending to be more female biased during the periods of higher CPUE. The higher catches achieved by using long dip nets may be related to the spawning behavior of Honmoroko in the inlet to the lagoon, indicating the importance of evaluating the recreational catches for the management of Honmoroko in Lake Biwa.

　To elucidate the molting growth of beni-zuwai crab Chionoecetes japonicus, molt increment (post-molt CW (carapace width) − pre-molt CW), growth rate (molt increment/pre-molt CW×100 (%)), and intermolt period were investigated by a rearing experiment using wild crabs collected from Toyama Bay, in a tank with running deep-sea water at the temperature of about 0.7℃. The data of 152 regular molts and 60 maturation molts by 142 males, and 115 and 39 of those by 92 females, were used for the analysis. Most (more than 90%) of molts occurred until 3 years from the start of the rearing experiment, although in the longest case molt started at 5.3 years. The growth increment increased with size for the CW range of 6.2–96.9 mm, however, the growth rate decreased for the larger crab. The decline of growth rate of females was more rapid than that of males. Intermolt periods increased with size, and a significant linear regression was obtained between intermolt periods and pre-molt CW. Intermolt periods became longer than one year at the CW of about 45 mm or more in both male and female crabs.

　This study investigated the causes of die-off of Ephinephelus akaara larvae. The die-off possibly occurs due to differences in body density of individuals with time in the breeding water. Therefore, we measured time-series changes in body density of larvae after they hatched. The mean body density of larvae was 1.023 ±1.387×10⁻³ g cm⁻³ after hatching in the same water that they were bred in at an age of 2 days and at 12:00. In addition, we calculated the oil globule and yolk sac volumes of larvae as time series. The results indicated that most of the individuals were exhausted after opening of the anus at an age of 1 day and at 12:00. Subsequently, the contraction of total length occurred until the age of 3 days and at 20:00. Our results suggest that the body density increases over time due to a decrease in the volume of larvae.

　This study focused on an aquatic oligochaete, Monopylephorus rubroniveus, which is found in high density at plum processing wastewater treatment plants, as a candidate animal for fish feed. We investigated the effective feed for culturing this oligochaete. When the sludge from the wastewater treatment plant was given, after 4 weeks of rearing the body length grew 5.4 times and the body weight grew 26.6 times larger than those of newly hatched young worm (body length 2.7 mm, body weight 0.040 mg). As a result of examining other materials replacing sludge, yeast showed the same level of growth ratio, growth rate and survival rate as sludge. We also found that sake lees and shochu lees, which are yeast-based food wastes, can be used as feed for the aquatic oligochaetes.