The fishermen had come for the giant clams, massive mollusks measuring as much as four feet across and weighing 500 pounds. Grinding their boat propellers against coral in the South China Sea, they excised the shells, leaving half-moon scars and broken reefs in their wake.

Even when giant clams became rarer and harder to find, they kept coming. Carved giant clam shells resemble elephant ivory and can fetch high prices in China, where they’re fashioned into jewelry and statues. They’ve also been plundered for the aquarium trade and for their meat.

Philippine authorities have seized about 133,000 tons of these increasingly rare shells since 2016, according to a new report by the Wildlife Justice Commission (WJC),