Ecuador is already debating whether to limit growing tourism on Galapagos and has expelled hundreds of illegal workers to protect the natural reserve after the United Nations warned last year that the site was in danger.

"It is obvious the control system has to be greatly improved," said Luis Suarez, the head of Ecuador's branch of Conservation International. "We need satellite control to know where people are, and better police intelligence to know more about the traffic of species and their organs."

Authorities don't know why the sea lions were butchered. Traffickers often kill animals to take organs in demand for traditional medicines. But these sea lions were untouched except for head wounds, officials said.

Ecuador's media also recently criticized local Galapagos authorities after showing images of one tourist holding a baby sea lion and another sitting on top of a massive tortoise in a violation of strict controls at the site.

The volcanic islands, located 650 miles (1,000 km) off Ecuador's coast, inspired British naturalist Charles Darwin's theory of evolution. Centenarian tortoises and blue-footed boobies live alongside 18,000 islanders who earn a living from fishing and tourism.

"The growing demand and the tourism market is imposing the rules of the game," said Eliecer Cruz, the governor of Galapagos. "We are working very hard to look for a new type of tourism in Galapagos."