Skipjack tuna samples were collected monthly at Shinkang fishing port, Penghu third fishing market and Penghu Suogang fixed net fishing market from January 2020 to October 2020. 329 samples (31-74.5 cm fork length; 0.6-8.7 kg) were collected in eastern Taiwan. The result of the chisquare test showed that there was a significant difference in the sex ratio in July, and no significant difference in other months. The result shows that the peak period of spawning in the eastern Taiwan waters is April to July. 36 samples (34.4-51.1 cm fork length; 0.76-2.96 kg) were collected at Penghu third fishing market and Penghu Suogang fixed net fishing market. The δ15N value is 9.80‰, the δ13C value is -17.92‰and the trophic position is 3.45 of the Taitung skipjack tuna. The δ15N value is 11.31‰, the δ13C value is -18.11‰and the trophic position is 4.07 of the Penghu skipjack tuna. It shows that theδ15N value of Penghu samples is higher than Taitung samples. However, there is no difference between Penghu and Taitung samples. The relationship between the δ15N value and the fork length is both not significant of the Taitung and Penghu samples, and this situation is often found in the waters near the land. According to the fishing method, it is divided into torch light net, set net and trolling line fishery for stable isotope analysis. It shows that the δ15N value is obvious differences among the fishing methods, with the set net the highest, the torch light net the second and the trolling line fishery the lowest. In total eastern samples were collected, of which 31.7% (n=101) contained identifiable prey. According to the index of relative importance (IRI), the most important prey species were Round scad (Decapterus sp.; IRI=2054.32) followed by Flyingfish (Cheilopogon sp.; IRI=609.02) and Cephalopods (Myopsina sp.; IRI=442.68). These preliminary results indicate that skipjack tuna feed predominantly on pelagic fishes in eastern Taiwan waters. In Penghu samples, five kinds of food organisms appeared in the stomach contents. According to IRI, the most important prey species were Leiognathus bindus (IRI=4371.85), followed by Clupeidae sp. and Engraulidae sp. (IRI=388.78). The complete mitochondrial D-loop sequence was used to analyze the bonito population along the coast of Taiwan. The results show that the population of skipjack tuna in Taiwan is quite stable and highly circulated. Haplotype is similar to other studies on NCBI. All samples show that their genotypes have weak clustering. 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 2020), another 15 were captured (recovery rate: 6.3%). Of which 3 electronic markers were recovered, but 1 did not interpret the information. Two skipjack tuna 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. 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. Skipjack tuna displayed repetitive bounce-diving behavior to depths between 50 and 300 m during the daytime. 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.