On 2 April 2015, the International Tribunal for the Law of the Sea (ITLOS) rendered its first full-bench Advisory Opinion. In its reply to the request of the West African Sub-Regional Fisheries Commission the ITLOS found that Arts. 62(4), 58(3), 192 of the United Nations Convention on the Law of the Sea contain obligations for a flag state to ensure that vessels flying its flag do not engage in illegal fishing in the exclusive economic zones of coastal states. The Advisory Opinion has widely been praised for bringing clarity to the inadequate international fisheries law regime. This article undertakes to analyze the ITLOS’s interpretive approach, expose interpretive deficiencies, and offer possible explanations for some of the outcomes where the ITLOS itself did not do so.