Senior Philippine officials on Thursday insisted the government will not release nine Chinese fishermen who were convicted of poaching in disputed waters, defying pressure from Beijing.

President Benigno Aquino's spokesman Herminio Coloma said the nine, who were convicted on Monday for catching endangered sea turtles, merely have to pay a fine in order to walk free.

"For the offence pertaining to possession of endangered species, the court imposed a penalty of payment of fines. Upon payment of the fines, they are deemed to have served the penalty fully, and there is no further impediment for them to leave the country," he told reporters.

Foreign Secretary Albert del Rosario stressed that it was the independent judiciary that found the fishermen guilty, not the government.

"We must respect the decision of the court," he said in a statement.

The nine were found guilty on Monday and fined $100,000 each for poaching with an additional 120,000 pesos ($2,730) fine for catching an endangered species.

The case has strained relations between China and the Philippines, who are engaged in a bitter territorial dispute in the South China Sea.

Filipino police said they found hundreds of sea turtles -- a protected species -- on board the fishermen's vessel when they arrested the group in May at Half Moon Shoal, located in a part of the sea claimed by both countries.

On Tuesday China called on the Philippines to release the fishermen, saying their arrest was a violation of Beijing's sovereignty.

Beijing claims almost all of the South China Sea -- which is home to crucial shipping lanes, vast fishing areas and potentially valuable mineral resources -- including areas close to the coastlines of other nations.

Its claims conflict with those of Brunei, Malaysia, Taiwan and Vietnam as well as the Philippines.

In March the Philippines filed a formal plea to the United Nations challenging China's claims in the South China Sea, but Beijing has rejected UN arbitration.

China previously refused to cooperate in the legal proceedings against the fishermen and failed to provide a defence lawyer or translator for them -- a move which prosecutors said delayed the proceedings.

If the fishermen do not pay the fines they can be imprisoned for about six months for each offence.

But since they have already served six months in jail while the trial was going on, they are deemed to have already served the sentence for poaching and must now only deal with the sentence for taking endangered species, Coloma said.

strs-mm/kjl