Dolphinfish ( Coryphaena hippurus ) is a highly migratory oceanic pelagic fish found worldwide in tropical, subtropical, and temperate waters. In East Asia, dolphinfish support economically important commercial fisheries, and are a shared resource among multiple countries, such as Taiwan and Japan. To urge Taiwanese dolphinfish fishery on achieving the certification of fishery improvement project (FIP) to ensure the US export markets, relevant studies for dolphinfish implemented by scientists were necessary as evidence. For the tagging experiments, one dolphinfish was tracked for periods of 30 days reaching depths 0-70 m, and experiencing temperatures ranging from 21.4-30.1°C. This fish spent >50% of their time near the surface and made more extensive vertical movements during nighttime than daytime, but vertical movements were largely confined to the mixed layer and did not cross the thermocline. The depth distributions of the tagged fish appeared to be limited by a 6 °C (i.e., >90% of movements were within 6 °C of the warmest water) change relative to sea surface temperature. Overall, tagged dolphinfish primarily inhabited near-surface habitat and vertical movements are limited by the depth of the mixed layer. This study found that dolphinfish dove deeper and for longer durations at nighttime, rather than daytime. Diel dive pattern may relation feeding opportunities when prey are aggregated and (or) may have evolved to avoid predators. We integrated the operation and VDR data of sample vessels in recent years to develop a model for estimating the fishing hours based on fishing trips. The estimated historical fishing hours of vessels were used to calculate the CPUE of mahi-mahi in the eastern Taiwan waters. In addition, the cluster analysis was adopted to identity the fishing methods of vessels and the clusters were further incorporated into the model as a factor related to targeting species of fishing operations. The trends of standardized CPUE indicated that the highest CPUE values occurred in the second quarter and there were often high CPUE values in the fourth quarter. However, the CPUE revealed a decreasing trend in recent years. 225 muscle samples were collected from PonHu, SuAu, TungKang and Shingkang in Taiwan and other waters including Nagasaki in Japan. Majority of samples from Shingkang in 2013 and 2014 were preliminary analyzed using sequencing data. In addition, samples collected from others waters such as Japanese area and eastern Pacific Ocean are desired for the further investigation of genetic population structure. For the preliminary results, we focus on the comparison the genetic differentiation of the dolphinfish samples collected from Taiwan and Japan waters. We surveyed the pattern of genetic differentiation using 766 bp of sequence of the mtDNA ND1 for 225 individuals. We report significant genetic differentiation between the collection from Taitung 2013 (spring season, n= 42) and the collections from PonHu (n= 13), and Nagasaki (n= 29). These results show genetic heterogeneity between Taitung 2013 and Nagasaki, Japan. However, the rest of samples collected from Taitung didn’t show the similar differentiation pattern. Therefore, in future studies, sample sizes and geographic coverage should be increased to resolve the population structure of dolphinfish.