Takefumi Fujimoto, a postdoctoral fellow at the University of Tokyo, visited the NatuRE Policy Lab and presented his research on bycatch species with commercial values in Japan’s purse seine fishery. In 2023, large- and medium-scaled purse seiners in the Sea of Japan and the East China Sea introduced individual quotas (IQ) for horse mackerel and chub/blue mackerel. Because of the two fishes' biological migration patterns, chub/blue mackerel, which has a commercial value, are often caught together with horse mackerel. Takefumi first models why bycatch species with commercial values could constrain the use of IQs for other targeted species more severely. Using panel data on daily catches and IQ usage rates at the fleet level, he then empirically shows that the tighter the IQ for chub/blue mackerel, the more constrained the catch of horse mackerel. Combining a correlated random effects Tobit model with a control function approach, he shows that an increase in the IQ usage rate for chub/blue mackerel reduces daily catches of horse mackerel, leading to underutilization of IQs for horse mackerel.