Despite international waters representing nearly two-thirds of the world's oceans, only 1.2% is protected.
Environmental campaigners have called it a "missed opportunity".
The last international agreement on ocean protection was signed 40 years ago in 1982 - the UN Convention on the Law of the Sea.
That agreement established an area called the high seas - international waters where all countries have a right to fish, ship and do research.
Marine life living outside of the 1.2% of protected areas are at risk of exploitation from the increasing threats of climate change, overfishing and shipping traffic.