Dolphins’ playful social habits form bonds, but spread the virus

FILE-This photo shows dolphins off the coasts of Port-Leucate on March 3, 2022. (Photo by RAYMOND ROIG/AFP via Getty Images)

Three young male dolphins simultaneously break the water’s surface to breathe – first exhale, then inhale – before sliding back under the waves of Chesapeake Bay.

“A perfect synchronization,” said Janet Mann, a dolphin researcher who watched from a small skiff.

Synchronized breathing is something dolphins often do with close friends, like these males, or mothers and calves do together, Mann said. It’s a way of affirming the relationships that are so important to these highly intelligent and social mammals, like a handshake or a hug between humans.

“It says, ‘We’re together,'” says Mann, who is based at Georgetown University.

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While such close contact is essential for social bonds with dolphins, sharing space and air can also quickly spread disease.

Mann and other scientists are trying to understand how a highly contagious and deadly disease called cetacean morbillivirus — related to measles in humans and first discovered in Virginia and Maryland waters — can spread rapidly among dolphins along the Atlantic coast, such as the did from 2013 to 2015.

During that outbreak, more than 1,600 dolphins washed up on beaches from New York to Florida, according to the National Oceanic and Atmospheric Administration. In total, an estimated 20,000 dolphins died from the virus, and the region’s coastal dolphin population shrank by about 50%.

“It’s a lot like COVID — it’s respiratory” in how it spreads, Mann said. “When dolphins breathe together on the surface, they share respiratory droplets, just like we do when we talk or cough to each other.”

She realized that the key to understanding rapid virus transmission was pinpointing dolphins’ social networks, just as public health authorities have been monitoring the COVID-19 pandemic.

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To understand how disease circulates in social animals — such as humans, dolphins or chimpanzees — scientists need to examine not only the biology of a virus, but also how vulnerable populations interact, said Jacob Negrey, a researcher who studies animal viruses at the Wake Forest School of Medicine.

“Contact networks represent a double-edged sword,” he said. “Your friends you need are also the people most likely to make you sick.”

Dolphins are extremely playful animals and often swim close to each other, sometimes even using their fins. “We call it hand-in-hand,” says Mann, who also leads the nonprofit Potomac-Chesapeake Dolphin Project.

While many people casually refer to a “pod” of dolphins, Mann dislikes the term because it implies a stable group, such as a pack of wolves. What she has observed over 35 years of dolphin research in the US and Australia is that while dolphins have close friends, they regularly come and go to check on others.

In the Chesapeake Bay area, to track how dolphins mingle, the scientists had to distinguish more than 2,000 dolphins, mostly by distinctive shapes and markings of their dorsal fins.

“To me it’s like a face,” Mann said. “I joke with my students that if they wore dorsal fin hats, I’d remember all their names.”

On light-wind mornings, the scientists set out in an 18-foot (5.5-meter) skiff to look for dolphins near where the Potomac River flows into the bay.

A trained eye can spot light splashes on the water a mile away, or catch the glint of sunlight on a fin or tail.

“I’m looking for dark objects breaking through the water’s surface,” said Georgetown biologist Melissa Collier, scanning the horizon through binoculars.

Suddenly she yelled for the boat to slow down and pointed with one hand. “Dolphins at the pier, close to the shore.”
Ann-Marie Jacoby, a marine and naturalist at Duke University, peered through binoculars, then smiled in recognition. “We’ve got Abe Lincoln and his buddy Andrew Jackson,” she called out.

Because the Potomac runs through Washington, the researchers named many dolphins after American historical figures.

“It’s so nice to find dolphins that we know,” Jacoby said. “These males have been seen together regularly over the past year.”

The scientists can easily spot a few hundred dolphin fins by sight.

To identify lesser-known dolphins, they photograph their dorsal fins and compare them to a catalog of fins created since 2015 — essentially a Facebook for dolphins.

“Andrew and Abe just synchronized,” Collier said, taking notes as another dolphin approached.

James Buchanan was now less than 5 meters from the other dolphins, which Collier said were close enough for the spread of disease. “The drops of their breath can be shared.”

All three dolphins surfaced and breathed together, then disappeared beneath the waves.

“This is typical male behavior,” Mann says. “The males remain quite in tune. The females synchronize, but not as regularly. They usually synchronize with their offspring.”

That difference in behavior may help explain why males died in greater numbers during the most recent outbreak of cetacean morbillivirus — a hypothesis the researchers are exploring.

While Atlantic bottlenose dolphins are not threatened, NOAA considers their coastal populations “depleted,” meaning “below optimal sustainable population.”

Outbreaks of the virus occur here every 25 years. And they hit dolphins and their closest marine relatives elsewhere, including some endangered whale species.

University of Hawaii researcher Kristi West called the disease — which causes skin lesions, pneumonia, brain infections and a suppressed immune system — “the most significant threat to dolphins and whales on a global scale.”

Although viruses occur naturally in the wild, human disturbance of marine habitats has made animals more vulnerable. “The disease becomes an even greater threat when we combine it with other stressors facing dolphins and whales around the world,” West said.

From the boat on the Chesapeake, the water looks clear and calm.

“We don’t see what’s under the surface,” Mann said, casting a gloomy look down. “But carbon and plastic and prey depletion – these are all things that threaten the animals,” along with warming oceans from climate change.

Such tensions weaken dolphins’ immune systems. “So they are extremely vulnerable to virus outbreaks,” she said.
Collier hopes their research can be used to predict when epidemics might occur, and then use that information “to try and implement policies in areas where human disturbance is really high.”

Perhaps that could mean limiting noisy boat traffic or road pollution when outbreaks are underway or likely, she said.
It is difficult to be on the boat for long, as the scientists continue to search for dolphins.

“A baby!” Mann suddenly screamed with joy as some dolphins approached.

In the first few months after birth, dolphin calves have visible lines on their sides because they are folded in the womb.
Jacoby recognized this particular mother’s fin, referring to the dolphin — not the former US Senator from Texas — then let out a cheer: “Kay Bailey Hutchison has a baby with fetal lines!”

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