This project is from August 26 to September 8, and a total of 14 days went to Japan for a visiting program. The main purpose is to go to International Research Institute of Far Seas Fisheries, Fisheries Research and Education to study the population characteristics of the skipjack tuna, including the use of tagging experiment to analyze the behavior of skipjack tuna in the Pacific Northwest, and to combine future research results with reproductive biology. And analysis of spawning activities in Taiwan and Japan, integrated analysis of the tagging results to improve the development of related research and provide important parameters for stock assessment. From December 2017 to March 2019, a total of 239 signs were released in the eastern sea area of Taiwan, and 148 electronic recorders were deployed. Up to now (November 2019), another 15 were captured (recovery rate: 6.3%). Of which 3 electronic markers were recovered, but 1 did not interpret the information. From December 2017 to March 2019, a total of 239 skipjack tuna were released off eastern Taiwan, and 148 archival tags were deployed. Up to now (November 2019), another 15 were captured (recovery rate: 6.3%). Of which 3 archival tags were recovered, but 1 did not interpret the information. Two skipjack tuna (43 and 44 cm FL, #5885 and #6312, released on 2018/12/16 and 2019/3/14, respectively) were caught by trolling boat around the FAD near Green Island (southeastern Taiwan) deployed with archival tag (Lotek LAT2910), were recovered near the released area and provided in aggregate data archiving 26 and 31 days-at-liberty. The tagged skipjack tuna dove deeper during daytime than at nighttime (p<0.001). There is significant difference during daytime and nighttime in temperature and depth. Fish#5885 habited depth and temperature from 0-271m, 13.1-27°C. Fish#6312 habited depth and temperature from 0-310.6m, 13.2-28.3°C. Skipjack tuna displayed repetitive bounce-diving behavior to depths between 50 and 300 m during the daytime. During that dive of two fish, the ambient temperature reached a low of 13 and 13.2°C, and the peritoneal cavity temperature reached a low of 17 and 18.5°C. Our findings are the first fishery-independent observations on the degree of vertical habitat of skipjack tuna in eastern Taiwan, provide about the interaction an ecological and fisheries.