Thousands of crustaceans were found dead off the coast of Lima following the mystery mass death of dolphins and pelicans, the Peruvian Navy said Friday.

The cause of death is under investigation, said Industry and Fishing Minister Gladys Triveno, warning that "it would be premature to give a reason for this phenomenon."

The Navy said it presented a report on the find to the Agency of Environmental Evaluation and Control to determine the cause.

Biologist Yuri Hooker of Cayetano Heredia University said the species found on Pucusana Beach, 60 kilometers (37 miles) south of Lima, was a type of red krill about three centimeters (1.2 inches) long.

"They live mostly along the coast of Chile up to the coast of northern Peru. What is happening is that these crustaceans are being affected by the warming of Pacific waters in the north of the country," he said, adding that the phenomenon occurs "with some frequency."

Hooker explained that the warmer temperatures led the shrimp-like creatures that usually live far away from the coast to move in closer to land, where they died.

Nearly 900 dolphins washed up along Peru's northern coast between February and April. A government study said the marine mammals died of natural causes, while environmental groups insist the massive toll was linked to offshore oil exploration in the area.

Peruvian officials have suggested that the dolphins, along with 5,000 dead sea birds -- mostly pelicans -- died due to the effects of rising temperatures in Pacific waters, including the southern migration of fish eaten by the birds.