How does UNCLOS regulate naval blockades and maritime sovereignty during armed conflicts?

UNCLOS is not a complete rulebook for naval warfare. It sets out maritime zones and navigation rights; the legality and conduct of a blockade are addressed mainly by the law of naval warfare and other rules of international law.

What UNCLOS says about maritime zones

A coastal state has sovereignty over its territorial sea, subject to UNCLOS and other international law. Foreign ships generally retain a right of innocent passage, although passage that is not innocent may be challenged under the Convention. UNCLOS also lets a coastal state temporarily suspend innocent passage in specified areas of its territorial sea when essential for security, provided the suspension is properly published and applied without discrimination. That provision is not, by itself, a general authorization to impose a wartime blockade.

Beyond the territorial sea, the coastal state does not have full sovereignty over the exclusive economic zone (EEZ). It has specified sovereign rights, especially over natural resources, while other states retain navigation freedoms. On the high seas, navigation is generally free. In international straits, transit passage cannot be suspended under UNCLOS; archipelagic sea-lanes passage is likewise protected from suspension.

Where blockade rules come in

A naval blockade is principally governed by the law of naval warfare, including customary international law; the San Remo Manual is a widely cited, non-binding restatement of many of those rules. In general, a blockade must be declared and notified, effective, applied impartially, and directed against the enemy rather than neutral shipping as such. It must not be used to starve civilians or deny them objects essential to survival, and expected civilian harm must not be excessive in relation to the anticipated military advantage.

Those rules do not displace UNCLOS protections or give a belligerent sovereignty over another state's waters. A blockade cannot simply erase neutral states' maritime rights, and its location and enforcement must be assessed alongside rules on neutral waters, navigation, and the prohibition on the use of force. In particular, transit passage through international straits and the rights of ships in an exclusive economic zone raise questions distinct from control of a state's territorial sea.

So the short answer is that UNCLOS defines the maritime rights and zones involved, while separate armed-conflict rules determine whether a blockade is lawful and how it may be conducted. The facts matter: where the blockade operates, what it targets, how it is enforced, and its effects on civilians and neutral shipping.