Peru dolphin deaths still a mystery

The mystery surrounding the deaths of almost 900 dolphins in Peru has deepened, as the government said human activity was not to blame but couldn't pinpoint a natural cause for the massive die-off.

A final report from the Peruvian government's Ocean Institute said the dolphins didn't die from lack of food, hunting by fishermen, poison from pesticides, heavy metal contamination, infection or virus, according to Reuters. It also said there was no evidence linking seismic offshore exploration by oil companies to the mass dolphin deaths.

More from GlobalPost: Peru pelican deaths: Government declares health alert, says keep off northern beaches

Peru's officials have suggested that the dolphins, along with almost 5,000 dead pelicans, died because of the effects of rising temperatures in the Pacific waters, but couldn't come to a final conclusion about cause of death, reported Agence France-Presse.

"It's not the first time that this has happened," said Gladys Trevino, Peru's Production Minister, pointing to what she said were similar mass dolphin die-offs in Australia, New Zealand and other countries.

Some of Peru's leading scientists complained that the government was too late in gathering samples from the dead dolphins, which made it harder to determine their cause of death because the tissue being tested was badly decomposed, according to Fox News.

More from GlobalPost: Peru's massive dolphin die-off sparks concern over oil search

The Ocean Institute is said to have based its findings on only two dead dolphins that were collected in mid-April, while the first samples environmental group Orca said it tested were gathered on February 12, reported Bloomberg BusinessWeek.