This study aimed to understand the size-specific spatiotemporal dynamics of bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean from 1991 to 2017. A spatiotemporal delta-generalized linear mixed model was applied to catch rate data by size class collected from a Japanese longline fishery. The results showed that the density of bigeye tuna varied spatially across the eastern Pacific Ocean, with spatial segregation by size. The mean predicted density by size in the study area (100–150 °W, 10 °S–10 °N) indicated that adult fish (fork length (FL) > 152 cm) were mainly distributed in the middle of this study area, 110–140 °W in both hemispheres. For the intermediate size stage (FL > 115 to < = 152 cm), a high-density area was found in both the western and eastern parts, but mainly in the northern hemisphere and east of 120 °W. A high-density area of the juvenile stage (FL < = 115 cm) was found in the southwestern part of the study area. Spatial restructuring by size in response to El Niño and La Niña was also observed. El Niño and La Niña caused adult fish to distribute in the eastern and western EPO, respectively, and the smaller fish were distributed in the opposite area. Oceanographic conditions affect fish distribution and movement differently according to size, and the trends in relative abundance by size were different. We discuss the reasons for the segregation by size and the different responses of each fish size category to oceanographic conditions.

本研究旨在了解 1991 年至 2017 年东太平洋大眼金枪鱼 (Thunnus obesus) 特定尺寸的时空动态。应用时空三角洲广义线性混合模型，按从日本延绳钓线收集的尺寸等级收集捕获率数据渔业。结果表明，东太平洋大眼金枪鱼的密度在空间上存在差异，并因大小而异。研究区域（100-150°W，10°S-10°N）的平均预测密度表明，成年鱼（叉长（FL）> 152 cm）主要分布在该研究区域的中部，两个半球均为 110–140 °W。对于中等大小阶段（FL > 115 to < = 152 cm），在西部和东部都发现了高密度区域，但主要在北半球和 120 °W 以东。在研究区的西南部发现了一个高密度的幼鱼阶段（FL < = 115 cm）。还观察到了响应厄尔尼诺和拉尼娜的大小空间重构。厄尔尼诺和拉尼娜分别导致成鱼分布在 EPO 东部和西部，较小的鱼分布在相反的区域。海洋条件对鱼类分布和运动的影响因大小而异，不同大小的相对丰度趋势也不同。我们讨论了按尺寸划分的原因以及每个鱼类尺寸类别对海洋条件的不同反应。厄尔尼诺和拉尼娜分别导致成鱼分布在 EPO 东部和西部，较小的鱼分布在相反的区域。海洋条件对鱼类分布和运动的影响因大小而异，不同大小的相对丰度趋势也不同。我们讨论了按尺寸划分的原因以及每个鱼类尺寸类别对海洋条件的不同反应。厄尔尼诺和拉尼娜分别导致成鱼分布在 EPO 东部和西部，较小的鱼分布在相反的区域。海洋条件对鱼类分布和运动的影响因大小而异，不同大小的相对丰度趋势也不同。我们讨论了按尺寸划分的原因以及每个鱼类尺寸类别对海洋条件的不同反应。