The bodies of 15 sea lions have been found in Ecuador's Galapagos Islands with their teeth and sexual organs extracted.
It is thought the removed teeth and organs will be put on sale in Asian black markets as aphrodisiacs.
The carcasses were discovered after Galapagos National Park officials received an anonymous tip.
Some 25 mutilated sea lions had been left on the southern shore of San Cristobal, the easternmost island in the remote Pacific archipelago.
"Eyeteeth and male sexual organs were removed from the sea lions, and all had fractured skulls," park officials said. They confirmed that four females and 11 males had been killed and that rangers were searching for others.
"Presumably, they were sacrificed so their parts could be sold on black markets in Japan," where the organs are sold as aphrodisiacs, the statement said.
No hunting and limited fishing is allowed in the Galapagos Islands, 600 miles west of the Ecuadorean mainland.
The islands are known for their variety of rare and exotic animals, whose unique characteristics were made famous by Charles Darwin, the 19th century naturalist.
Investigators believe the sea lions, which have no natural predators on land, were dumped in the ocean after they were mutilated and then washed back ashore by the currents.