Relationship between escape behavior of juvenile Pacific bluefin tuna and bag net shape of set net

Abstract

定置網におけるクロマグロの漁獲量の調整方法の開発は課題の1つである。その調整方法の1つとして網から自然逃避しやすいと言われているクロマグロの行動特性を利用することが考えられる。そこで，クロマグロ小型魚の箱網外への逃避と，漁場の流速，箱網底面の深度，経過時間，尾叉長の関係を調査した。その結果，潮流による箱網底面の吹き上がりがクロマグロの自然逃避を促すことがわかった。箱網深度よりも定置網漁業での利用機会が多い潮流の情報は，クロマグロ小型魚の漁獲コントロールに役立つ可能性がある。Controlling the catch of Pacific bluefin tuna in set nets is an important issue in stock management of the species in order to comply with quotas under international regulations. Bluefin tuna, once inside set net gear, tend to escape naturally due to the structure of set net gear before landing. Investigating the shape of the set net depending on oceanographic conditions, which are relevant for natural escape, may yield clues for controlling the catch. We therefore studied the relationship between fishing conditions and escape behavior of Pacific bluefin tuna by a tagging experiment. The test results were analyzed by a generalized linear model and the best model was selected by Akaike’s information criterion. The explanatory variables were body length of Pacific bluefin tuna, tidal current velocity, bottom of the minimum bag net depth, and elapsed time. The results showed that escape of Pacific bluefin tuna was affected by minimum bag net depth and tidal current speed, because the tidal current raised the bag net bottom and reduced the swimming space for the tuna. These results may be useful for future resource management of Pacific bluefin tuna in set nets.公開日: 2025-07-10journal articl