The global issue of Sustainable marine fisheries is considered as common concern to humankind. The emergence and persistence of noncompliant fisheries practices conveniently labelled ‘Illegal, Unreported and Unregulated fishing’ (IUU fishing), is of particular concern for the international community, regional fisheries management organizations and coastal states. The International Tribunal for Law of the Sea (ITLOS) in its first full-bench Advisory Opinion in 2015 found that Arts. 62(4), 58(3), 192 of the United Nations Convention on the Law of the Sea (UNCLOS) contain obligations for a flag state to ensure that vessels flying their flags do not engage in illegal fishing in the exclusive economic zones of coastal states. By this explanation, the Advisory Opinion initially has clarified the inadequate international fisheries law regime through ITLOS interpretive approach, which this paper attempts to examine by applying an exact legal scrutiny. The framework set by the Tribunal may allow States affected by IUU fishing, to exert greater pressure on flag states, particularly flag states of convenience, that do not comply with their responsibilities under UNCLOS. This paper suggests that the regulations on IUU fishing under international law should be enhanced and revised in order to draw an appropriate solution suitable for sustainable fisheries management.