How two shipments of scalloped hammerhead shark fins managed to slip out of Costa Rica and into Hong Kong last winter remains a mystery as no airline is admitting to carrying the cargo. For now, conservationists are attempting to piece together the trail of the shipments and are pointing a finger at package delivery company UPS for its possible involvement, though the company denies the claims. They have launched a petition to press the firm to follow the practice of more than 30 airlines and ban transport of shark fins. In just two months, the petition , started by diver Chris Maddeford , has amassed more than 130,000 signatures demanding that UPS chief executive David Abney take action. Read more: Hong Kong needs to step up checks on shark fin trade after Costa Rica shipments found slipping under the radar, activists say A 411kg cargo of dried shark fin from both the scalloped and smooth hammerhead shark species left Juan Santamaria International Airport on December 22 with Hong Kong marked as its destination. American Airlines had confirmed in April that it had transported the December stock of fins to the United States. It later bowed to pressure from conservationists to stop commercial shipments of shark fins. It remains unknown which airline took the shipment to Hong Kong. But Costa Rican activist group Pretoma suspects UPS, given that it is the only company with a warehouse in the country. "We only know that fins are stored at the UPS plant and that they leave Costa Rica on UPS flights to Miami," it said. A UPS spokeswoman said the company had so far had not been provided with information to substantiate allegations of illegal activity posted on social media. Asked whether UPS had facilitated the December shipment to Hong Kong, she said shipping information of its customers was proprietary but if the company was made aware that contents were illegal, it would involve the relevant authorities. "When the company becomes aware of a shipper attempting to use the company's network for such items, UPS takes appropriate action ranging from terminating service contracts to providing information to law enforcement," she said. Correction: An earlier version of this story incorrectly referred to petition author and diver Chris Maddeford as UPS chief executive. It was Maddeford who initiated the petition. David Abney is the company's CEO.