In the Philippines, about 200 tonnes of illegally harvested giant clam shells, worth about $ 25 million (£ 18 million), were confiscated.
Seizures are one of the largest transports of endangered species in history.
Four suspects were arrested on an ecologically protected island in Palawan.
Tridacna grow over 1 meter in diameter and weigh up to 250 kg. They are considered essential to the local marine ecosystem.
The Philippines is home to most of the world’s largest tropical clams.
Jobic Fabello, a spokesman for the Parawan Sustainable Development Council, said the seized shells contained the world’s largest clam, Tridakna gigas.
“Depriving giant clams from their natural habitat is a form of intergenerational crime,” he told Agence France-Presse.
“It will have a permanent impact on marine ecosystems and future generations will be deprived of the benefits that come from it,” he added.
Tridacna gigas contains seaweed, the food source for many human species of fish. They are becoming increasingly vulnerable to poaching, both in meat and shells, which are used in place of ivory in jewelry and ornaments.
In the Philippines, killing an endangered species can result in imprisonment of up to 12 years and a fine of up to 1 million pesos (£ 15,000).