Authorities unearthed 336 pieces of shells on the shore of Bugsuk island in Palawan province on last Wednesday, a Philippine Coast Guard statement said.

No arrests were made over the cache, worth an estimated 8.1 million pesos ($145,000), the statement added.

The illegal trade of giant clam shells persists due to high demand in China and Europe, Jovic Fabello, spokesman for the Palawan Council for Sustainable Development told AFP.

"This has become a substitute for the ivory trade" following widespread bans on the trade of elephant tusks, said Fabello, whose agency is tasked to protect the Palawan region's biodiversity.

Giant clams, including Tridacna gigas which may grow to 1.5 metres (nearly five feet) in diameter and weigh more than 200 kilograms (more than 440 pounds), are a protected species in the Philippines.

They play a key role as food, shelter and building blocks in coral reef ecosystems where fish populations spawn.

A study released last year by the group Traffic, which monitors the illegal global trade of protected species, found the Philippines seized more than 121,000 tonnes of giant clams between 2003 and 2022, accounting for 99.8 percent of giant clams seized in trafficking incidents in Southeast Asia during that time.