Customary International Law and the Law of the Sea

The United Nation Convention on the Law of the Sea (UNCLOS) will celebrate in 2022 its forty’s anniversary. Qualified as “package deal”, it is the most “comprehensive document ever adopted by the international community”. The convention strengthened the purpose of customary international laws by codifying its provisions and by creating new ones.

International Law Regulation

The Statute of the International Court of Justice (ICJ) considers as a source of law “international customs, as an evidence of general practice accepted as law”. Two conditions must be met in order to establish a legally binding rule of customary international law. First, it must be a general and consistent practice adopted by States. The second condition, “opinio juris”, requires that the custom should be considered “as State practice amounting to a legal obligation”. A rule considered as customary will therefore be binding to all States unless they persistently objected to its application.

Initially the sea was ruled by a “laissez faire” regime subjected to European powers’s trade imperatives and disputes. The “basic rules of the law of the sea were designated by customary law”, but the increasing use of the oceans for navigation and fishing purposes led to the first maritime legal concept . In the 20^th century, the International Court of Justice has qualified international law of the sea’s provisions as customary international law. Consequently, these rules became binding to the international community. In 1958, the four Geneva Conventions of the law of the sea have set the first codified legal framework applicable to the ocean. Again, the ICJ ruled that some of the Conventions’ provisions should be addressed as customary, such as the baseline limitation or the principle of sovereign immunity of warship.

In the Continental Shelf Case (Libya v. Malta), the ICJ defined the “three role multilateral treaties can assume in relation to custom: recording function, defining function and a developing function”. UNCLOS, which was adopted in 1982, fulfilled such purpose. Qualified as a reflection of customary international law , the Convention codified and crystalized provisions already considered as customs by the ICJ. However, it also incorporated new subjects, such as environmental issues and disputes settlement, which could generate new customary international law. In the North Sea Continental Shelf case (1969), the ICJ stated the three conditions under which treaty provisions could be addressed as customary

Law of the Sea ratification

The extensive ratification UNCLOS combined by the customary statute of its provisions contribute to standardization of the law of the sea around the world. For example, despite not being part of UNCLOS, the United-States comply with its customary provisions and is an advocate for its rightful application through research and scholars.

In the 21^st century, customary international law is not obsolete as it enables State to share a common set of binding rules and to prevent legal vacuum.

In nowadays, the notion of fishing or navigation customary rights is oftenly used by States in order to support coastal States sovereignty or sovereign rights over a maritime area. However, an established customary right in international law of the sea, is not without consequences and should be understood and used cautiously.