More than 400 dead dolphins were found last month on the Pacific Ocean beaches where twice that amount were encountered in 2012, Peruvian officials say.
Authorities never established the cause of death in 2012. They are doing autopsies now on the dolphins found in January in the Lambayeque region on the northern coast.
Technician Jaime de la Cruz of Peru's IMARPE marine life agency said about 220 dead dolphins were found the last week of January, the rest during the previous three weeks.
De la Cruz said autopsy results were expected in two weeks. Exams would focus on lungs, kidneys and livers.
Autopsies of some of the more than 870 dolphins found in 2012 were inconclusive. Speculation ranged from biotoxins in the sea to seismic testing to an unknown ailment.
Yuri Hooker, director of the marine biology unit at Cayetano Heredia University said that in other parts of the world dolphin deaths generally were caused by environmental contamination when the sea mammals eat fish or other smaller species filled with toxins. Hooker said others died after ingesting discarded plastics floating in the sea.
The marine biologist said that in Peru determining the death of dolphins was "complicated" because government laboratories only had three or four of the world's 100 or so reagents, or substances or compounds, that can be used for determining the animals' cause of death.