Story highlights "More investigation needs to be done," says a marine biologist

Official: The dolphins were found over a 220-kilometer (137-mile) area of coastal Peru this year

The dolphins were not caused by starvation or poisoning with pesticides, officials say

Dozens of dolphins have also washed up in the United States and Brazil this year

Environmental authorities are investigating the deaths of more than 800 dolphins that have washed up on the northern coast of Peru this year.

The dolphins may have died from an outbreak of Morbillivirus or Brucella bacteria, said Peruvian Deputy Environment Minister Gabriel Quijandria, according to Peru's state-run Andina news agency. Speaking to CNN, he said he expects test results to be ready within the week.

"Right now, the most probable hypothesis is that it's a virus outbreak," he said.

Quijandria said Thursday that 877 dolphins have washed up in a 220-kilometer (137-mile) area from Punta Aguja to Lambayeque, in the north of the country.

More than 80% of those dolphins were found in an advanced state of decomposition, making it difficult to study their deaths, according to Andina.

Earlier last week, the Peruvian government put together a panel from different ministries to analyze a report by the Peruvian Sea Institute (IMARPE). Officials have been able to conclude that the dolphins' deaths were not due to lack of food, interaction with fisheries, poisoning with pesticides, biotoxin poisoning or contamination by heavy metals.

"When you have something this large, my gut would tell me that there's something traumatic that happened," Sue Rocca, a marine biologist with the Whale and Dolphin Conservation Society, told CNN. She floated a number of number of possibilities as to what could have killed the animals, including acoustic trauma, but concluded that investigators just don't know yet.

"More investigation needs to be done," she said.

The dolphin deaths in Peru are mark the third set of high-profile strandings in about two months.

In February, 179 dolphins --108 of which were dead -- washed ashore in Cape Cod, in eastern United States, according to the International Fund for Animal Welfare. Marine biologists are still trying to determine the cause of those deaths.

In early March, amateur video taken from a beach in Rio de Janeiro, Brazil, showed more than 30 dolphins on shore. In that instance, all dolphins were safely returned to the sea.