Oysters have been cultivated in Japan for a significant period of time, but the damage caused by typhoons has been a persistent problem. To address this issue, we studied the movement of Gros (oyster shell clumps attached to scallop) and hanging reams to identify the cause of typhoon-related damage. First, we constructed a Gro model and calculated the added mass coefficient and damping coefficient via a forced oscillation test. We also determined the drag coefficient from a drag test using the same model. Utilizing these coefficients as input parameters, we conducted a numerical analysis to study the behavior of the Gros and the hanging reams. In the numerical analysis, we subjected three hanging reams to waves, wind, and currents. We estimated the entanglement tendency of the hanging reams based on the distance between adjacent Gros. The results showed that the likelihood of entanglement of the hanging reams increased with a decrease in wave period for both regular and irregular waves. In addition, we discovered that the hanging reams’ entanglement was more likely when waves were incident in the direction where the chain was aligned.

An ultrasonic telemetry system was employed to monitor the bag net shape and volume of a large-scale set net off Oirase, Fukaura, Aomori Prefecture, during two fishing periods, namely May 15 to July 23, 2019, and May 18 to July 28, 2021. Two-dimensional electromagnetic current meters (logger version) were utilized to record the flow direction and velocity at three depths (10, 20, and 30 m) around the set net during the two fishing periods. The aim was to investigate the effect of water flow on the bag net shape and volume. The water flow direction around the set net was mostly toward the northeast, similar to the direction of the body net with respect to the bag net (46°NE). The flow around the bag net varied. Tidal currents did not significantly affect the flow. The water flow affected both the bag net shape and volume. The acoustic pingers on the bag net sometimes exhibited significant horizontal movement in addition to vertical movement. Generalized linear model analysis was used to express the bag net volume using flow components, with depth as a variable. The northeast flow component at a depth of 10 m increased the volume of the bag net, particularly in the fish-catching section, and that at depths of 20 and 30 m decreased the volume of the bag net.

本研究では，同じ形状のバケットを持つ軽量簡易グラブ採泥器とスミス–マッキンタイヤー採泥器の採泥効率について，実験室内の砂を敷設した円形水槽を用いて比較実験を行った。その結果，スミス–マッキンタイヤー採泥器の採泥率は約60.8%であった。一方，軽量簡易グラブ採泥器では，振動を与えて引き上げた場合の採泥率は約87.3%，振動を与えずに引き上げた場合は55.2%であった。また，軽量簡易グラブ採泥器の採集方法に関係なく，男女間で採泥効率に有意差が確認された。これは採泥器を引き上げる速さが採泥効率に影響を与えた可能性が考えられる。底生生物の採集にはバケット容量の約35%以上の採泥率が必要であることを考慮すると，本研究で比較したどの採集方法でも十分な採泥量を得られることを示しており，軽量簡易グラブ採泥器が野外調査における新しい調査方法の選択肢になると期待される。

The sporophytes of the warm temperate perennial kelp Ecklonia cava are known to mature from the second year. In some populations, however, thalli were recently suggested to mature within one year of germination in field observations, but the precocity was not directly confirmed in culture studies. In the present study, maturation rate of first-year sporophytes was examined for the first time. Free-living gametophytes were obtained from two wild populations in Moroiso and Jogashima Island, Miura Peninsula. The sporophytes derived from these populations were reared in a land-based tank (Exp. 1) or in open sea conditions (Exp. 2), respectively. The maturation rates of the sporophytes in the first year were 66% in Exp. 1 and 60% in Exp. 2. At the time of the maturation check, both stem diameter and total length were significantly larger in mature thalli than in immature ones (p<0.01, except total length in Exp. 1). Since the precocious thalli can mature earlier than the peak of browsing by herbivorous fishes (summer to autumn), they can be considered as candidates of a donor of zoospores to produce seedlings for restoration and expansion of the kelp beds.