Scientists Now Think They Know Why More Than 200 Dolphins Died In Brazil Bay


The same virus was responsible for the death of more than 1,000 bottlenose dolphins in 2013. Fogen/Shutterstock

Scientists believe they have discovered why more than 200 Guiana dolphins have died over the last few months in Brazil’s Sepetiba Bay, according to a new report by The New York Times

Scarred, emaciated, and bloated carcasses of Sotalia guianensis dolphins began surfacing late last year in a bay 40 miles (64 kilometers) west of Rio de Janeiro, sometimes as many as five a day. This population is believed to be one of the highest concentrations in the world and has now lost up to a quarter of its population.


Now, scientists have pinpointed the cause – an airborne virus related to the one responsible for measles in humans. Cetacean morbillivirus (CMV) affects the lungs, brain, and immune systems of marine mammals like porpoises, dolphins, seals, otters, and whales. All symptoms – which include skin lesions, rashes, disorientation, fever, as well as respiratory and brain infections – point to an "agonizing" death.

It’s not the first mass outbreak of CMV in dolphins. In 2013, more than 1,000 migratory bottlenose dolphins died from the same virus along the US Eastern Seaboard. In 1987, another outbreak occurred along the mid-Atlantic coast, killing almost 800 dolphins from New Jersey to Florida.

But Brazil's case is the first time the virus has been detected in the South Atlantic, and scientists want to know why.

The answer is a familiar one. Researchers believe that increased pollution and poor environmental planning have made the dolphins more susceptible to the virus. A mining company was in operation in the area in the mid-1990s, shutting down in 1998 after facing scrutiny for allegedly improperly disposing of waste runoff. Since then, the area has seen a development boom. Because they are an apex predator, cetaceans develop higher concentrations of toxins than non-apex predators by consuming exposed prey.


The virus is spread by inhaling respiratory particles and from direct contact between animals. It can enter through other entryways as well, such as the eyes, mouth, stomach, skin wounds, and urogenital track. Since dolphins are social mammals, outbreaks have the potential to spread quickly through interactions,

Pollution aside, accidental bycatch further threatens the survival of this population. Fishermen reported to the New York Times declines in populations of other bay marine animals. With dwindling populations of shrimp, sea bass, and sardines, fishermen have taken to larger nets that unintentionally trap dolphins as bycatch.

Scientists say the Guiana is a “sentinel” species. “When something is wrong with them, that indicates the whole ecosystem is fractured,” biologist Mariana Alonso told the newspaper. 

 [H/T: The New York Times]


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