Simulation of the capture process in set net fishing using a fish-schooling behavior model
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ORIGINAL ARTICLE Fisheries
Simulation of the capture process in set net fishing using a fish‑schooling behavior model Yuki Takahashi1 · Kazuyoshi Komeyama1 Received: 3 March 2020 / Accepted: 15 August 2020 © Japanese Society of Fisheries Science 2020
Abstract Generally, the catch efficiency (CE) of a set net is difficult to evaluate because it is affected by fish behavior. Therefore, to evaluate CE, we proposed a fish school behavior simulation model based on the boid model and applied it to a full-scale set net. The moving path of the fish school around the set net was simulated and visualized via the proposed method. From the moving path, three behaviors were identified: all individuals entering, all individuals escaping, and the school dividing in the entrance. A Monte Carlo simulation was conducted to evaluate the relationship between set net entrance shape and CE. The entrance net angle (θ) was considered over a range of 55°–90°. The ratio of fish entering the set net was ~ 60% at θ = 60°–90°, and significantly lower at θ = 55°. After entering the playground, over 80% of individuals entered the bag net. When θ = 60°, the ratios of fish escaping from the set net and entering the bag net were at their lowest and highest, respectively. Therefore, maximum CE was achieved at θ = 60°. We conclude that the proposed simulation method will contribute to more efficient set net design. Keywords Boid model · Catch efficiency · Fish schooling · Numerical simulation · Set net fishing
Introduction Set net fishing is an important fishing method in Japanese fisheries. The set net is a large-scale trap net that captures fish passively. Therefore, the catch efficiency (CE) of a set net is affected by fish behavior, which makes it difficult to evaluate. The bycatch from set nets has become a major problem in Japan. For example, the bycatch of bluefin tuna Thunnus thynnus has become a critical problem in Hokkaido, Japan. To reduce the bycatch from, or improve the efficiency of, set net fishing, a method for evaluating its CE and capture process is required. The CE and capture process of passive small-scale trap nets have been evaluated in several studies. Furevik and Løkkeborg (1994) evaluated CE for different baited commercial pot shapes and found that the important factors influencing CE were entrance accessibility, escape ratio, and water * Yuki Takahashi [email protected] 1
Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041‑8611, Japan
current around the pot. Li et al. (2006a) used a video camera to measure the behavior of arabesque greenling Pleurogrammus azonus at trap nets and found that catch ratios were highest at an entrance inclination angle of 34°; their field trials confirmed that catch ratios were greatly affected by trap net entrance shape, which was the single most important factor influencing CE (Li et al. 2006b). In a sea trial experiment, both catch amount and species were found to be affected by bag net shape and depth in Sagami Bay, Japan (Tang et al. 1982). Do
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