Scores of Dolphin Deaths Have Scientists Baffled

Mortalities have been mysteriously piling up in a bay near Rio de Janeiro, Brazil.

By Elaina Zachos
Published 10 Jan 2018, 17:11 GMT
Dolphins live in pods of up to 200 individuals and have close relationships.
Dolphins live in pods of up to 200 individuals and have close relationships.
Photograph by Noaa

Since mid-December, four or five dolphin carcasses have beached in Brazil each day. The cause of the deaths is still unclear, and the mortalities have conservationists baffled.

The Associated Press reports at least 88 gray dolphins have washed up in the Bay of Sepetiba, a coastal area about 45 miles west of Rio de Janeiro, since December 16. That's more than 10 percent of the bay's known dolphin population, which, at an estimated 800, may be the highest concentration of the species in the world.

Local conservation NGOs like the Boto Cinza Institute and SOS Botos are examining the carcasses' skin, blood, and bones, and scientists speculate a bacterium or virus is to blame. If a pathogen-related disease is diagnosed, Boto Cinza Institute chief coordinator Leonardo Flach tells StoryTrender, 70 to 80 percent of the population could die.

Often living in pods of up to 200 individuals, dolphins have close relationships, and a contagious illness could be devastating. Lab results are expected at the end of January.

"One day we will find dolphin corpses that are male and adults, and the next day, female and [young]. But most of them are skinny and with deep skin lesions," Flach tells ABC News.

Male Dolphins Offer Love Token To Females In Rare Video

Gray dolphins are listed as data deficient, but Flach says the species should be considered endangered. In the past, the mortality rate of the area's gray dolphins was about five each month, attributed to overfishing and chemical pollution. In 2016, 69 of the marine mammals were reported dead and in 2010, 32 dolphins were found dead.

Flach says areas surrounding Rio de Janeiro are very polluted and illegal dolphin hunting is rampant. The Bay of Sepetiba is bordered by condominiums, shipyards, and ports, but it's unclear how the development could be affecting the marine mammals.

"They are an endangered species," Flach says, "but with now this unknown disease, we hope to be able to put more pressure on the officials to help us to save the dolphins."

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