Size-specific spatiotemporal dynamics of bigeye tuna (Thunnus obesus) caught by the longline fishery in the eastern Pacific Ocean

•The density of bigeye tuna had large interannual variation across the tropical area of the EPO.•There was spatial segregation by size. Adult fish tend to be distributed in the equatorial area, and smaller fish are distributed in marginal areas.•Spatial restructuring by size in response to El Niño and La Niña was observed.•The trend of relative abundance index by size differed. 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