Tuna longline fishery is one of the most important fisheries in the offshore waters of Taiwan. The main species caught by the Taiwan tuna longline vessels including yellowfin tuna, bluefin tuna, bigeye tuna and albacore, and shark and billfish of the bycatch species. Yellowfin tuna is the species with highest catch in the Taiwan longline fishery, and it's total catch, CPUE, annual mean age and weight showed decline in the lately 4 year. The fluctuation of the yellowfin tuna resource needs to be surveyed continuously to prevent overfishing situation. This study will collect the weight, length, and fishing and sale data of yellowfin tuna caught by the Taiwan longline fishing vessels for analyzing it's resource dynamic. The sea surface temperature derived from the NOAA satellite is also collected for understanding the relationship between the fluctuation of yellowfin tuna resource and fishing ground environment in the offshore waters of Taiwan. Spatial distribution of yellowfin tuna larvae in the offshore waters of Taiwan will also be investigated in this study.