Academics are warning the South China Sea could face worsening environmental degradation over the next two decades because the countries that claim it are focused on competing over maritime sovereignty instead of working together on relief measures.

Between 333,000 and 1.6 million vessels fish the sea, said Zhang Hongzhou, research fellow with the China Program at the S. Rajaratnam School of International Studies at Nanyang Technological University in Singapore. About 3 million people depend on fishing in the sea for income.

Without intervention, by 2045 fish common in the sea will decline 9 to 59 percent due to over-fishing, acidification of the water and carbon dioxide emissions, the study said.

But turning calls from China and Southeast Asia for “joint development” are hard to turn into action, Zhang said.

“Let’s say even if they want to have some kind of fishery cooperation, it would be quite difficult for each party to agree on a set of rules,” Zhang said. “Even if you want to implement joint development, you have to agree on where to jointly develop.”