400 carcases found in single month on beach in Lambayeque region where more than 800 washed up in whole of 2012

More than 400 dead dolphins were found in January on the Pacific Ocean beaches of northern Peru where twice that number were encountered in the whole of 2012, officials have said.

Authorities never established the cause of the deaths in 2012. They are doing autopsies on the latest dolphins found 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 in the last week of January alone, the rest during the previous three weeks. Autopsy results were expected in two weeks. Examinations would focus on lungs, kidneys and livers.

Area where the dolphin carcasses were found. Guardian graphic

Autopsies of some of the more than 870 dolphins found in 2012 were inconclusive. Speculation ranged from biotoxins in the sea to seismic testing or an unknown ailment.

Yuri Hooker, director of the marine biology unit at Cayetano Heredia University, told the Associated Press that in other parts of the world dolphin deaths generally were caused by environmental contamination when they ate fish or other smaller species filled with toxins. Hooker said others died after ingesting discarded plastic floating in the sea.

The marine biologist said determining the death of dolphins was complicated in Peru because government laboratories had only three or four of the world's 100 or so chemicals that could be used for determining an animal's cause of death.