Tuna resource is abundant in central-western Pacific Ocean. Moreover, the easternwaters off Taiwan are noted as the migrating route and potential spawning grounds forPacific bluefin tuna. The aims of this study are (1) analyzing the historic catch statistics ofTaiwan's offshore longline fishery by the geographic information system (GIS) softwareto understand the spatial and temporal transitions characteristics of this fishery; (2)determining the possible key factors for the formation mechanism of the tuna's fishingground either by analyzing catch information obtained from the R/V and/or fishingvessels; or by the satellite surface temperature images and CTD information in situ.