Supreme Court Senior Associate Justice Antonio Carpio on Thursday said the Constitution prohibits the Duterte administration from inking a joint development with another state like China.

In an interview with ANC's Headstart with Karen Davila on Thursday, Carpio said the Constitution mandates the Philippine government to protect its exclusive economic zone (EEZ), including the ones awarded by the Permanent Court of Arbitration's (PCA) ruling.

READ: South China Sea tribunal: key findings

Carpio explained that the 381,000 sq.km. of marine space in the West Philippine Sea was granted by the court to Manila, and "there are no overlapping EEZ from China."

"The Constitution says that the state shall protect its marine wealth in the EEZ and reserve its use exclusively—use and enjoyment—to Filipino citizens," he said.

"So whether it’s President [Rodrigo] Duterte, President [Gloria] Arroyo, or any other president, that cannot be compromised. You cannot enter into joint development within our EEZ. It’s prohibited by the Constitution," he said.

But he noted, the Constitution allows for foreign companies to be contracted by the Philippine government to drill, and will be paid for the service.

"It cannot be a joint development state-to-state because that is our sovereign territory," he emphasized.

In the 497-page ruling, the international court also affirmed the freedom of navigation and overflight afforded to all nations, and Carpio is confident that other naval powers like the United States will do their part in enforcing the law.

"That part of the ruling will be enforced by the naval powers. They’ve already said that," he said.

He is optimistic that China will comply with the international court's decision, like the other 95% of losing parties in international arbitration.

"It has happened several times. The losing party will say ‘we will not comply,’ they’d hold demonstrations, they’d threaten to withdraw; but in the end, they comply," he said.

He acknowledged however that compliance will take time especially as China prepares its populace to accept the ruling. The Chinese, said Carpio, were taught in school that they own the area within the nine-dash line.

"It will take time, but it will happen in the end. So we have to look at this at a very long term perspective," he said.

REED BANK AND SCARBOROUGH SHOAL

The Reed Bank, which Carpio said may be the country's replacement for Malampaya, a natural gas field located in the West Philippine Sea from where the country sources most of its supply. It is estimated, however, that the Malampaya supply will run out in about a decade.

In 2015, tensions rose in the area as the Philippine navy found a large steel marker bearing Chinese inscriptions and hundreds of yellow buoys in waters near the Reed Bank.

"The ruling says the Reed Bank is ours. We will send there our survey ships again and please don’t harass them anymore. We will have to say that because we will have to alert them that we are sending our survey ships," he said.

Though direct communication lines must be left open between the two countries, the Philippines must take some steps prior to meeting with China, according to Carpio.

"We will have consultations with ASEAN friends—those who are also prejudiced by the nine-dash line but they are now free from the nine-dash line. We consult our friends and allies, and then we talk to China," he said.

Carpio added Manila must also discuss with Beijing steps for establishing a code of conduct for fishing in the Scarborough Shoal, which has been awarded as a common fishing ground.

"Let’s sit down with them first because the tribunal says it’s common and we have to lay down the rules for common use so there will be no skirmishes and no fighting by fishermen," he said.