Chesapeake dolphins thrill watchers, scientists | Wildlife and Habitat

DolphinWatch app user Rhiana Scholz captured this image of a pod of dolphins in the middle of the Chesapeake Bay on July 3, 2018.

Dolphins that visit the Chesapeake Bay in the summer have been listened to, photographed, identified by their dorsal fins and documented in a crowdsourced app for five years. But there is much more that scientists want to learn.

“Did they come earlier and stay later? It’s hard to say,” said Ann-Marie Jacoby, associate director of the Potomac-Chesapeake Dolphin Project and doctoral candidate at Duke University.

More people have been spotting Atlantic bottlenose dolphins on summer animal tours of the bay in recent years, but it could be for a host of reasons.

The Chesapeake DolphinWatch phone app, developed by the University of Maryland Environmental Science Center, is entering its fifth season to allow citizen dolphin watchers to record their findings. The application has nearly 10,000 users and has made many boaters aware of the presence of dolphins. Last summer, they recorded more than 1,000 sightings, with researchers confirming 70% of them, said project coordinator Jamie Testa.

“It’s been a big observation year for us,” she said.

Lauren Rodruigez, a graduate research assistant with the DolphinWatch program, used data from three years of tracking as the basis for a May 2021 report on trends in dolphin presence in the bay. The paper informs environmental impact assessments at military installations in the region, where dolphins may approach ships or coastal assets more frequently than previously thought.

“Before, the data showed that the dolphins only used the Lower Bay. But this data shows that they use the entire Chesapeake and [we] have to take that into account,” Rodriguez said.

In 2021, dolphins regularly appeared in Upper Bay off Rock Hall, MD. They also did well up the Chester River, Rodriguez said, “probably hunting prey and fishing boats, or just exploring.”

Dolphins on the Patuxent

This pair of dolphins was photographed in September 2019 in Maryland’s Patuxtent River by a DolphinWatch app user registered as Glen.

Potomac River researchers have documented dolphins as far upstream as the Governor Harry W. Nice Memorial Bridge, where U.S. Route 301 crosses the Potomac just south of Popes Creek, MD. It’s almost a 50 mile trip uphill, almost halfway to Washington, DC.

According to historical accounts, dolphins were spotted in 1884 all the way up the Potomac to the Aqueduct Bridge, just south of Georgetown University in DC. Still, people consider dolphin watching to be a relatively new phenomenon, especially in the Upper Bay.

“We hear from people, anecdotally, that they’ve lived here for 25 years and have never seen a dolphin until now,” Testa said.

She has spoken to others who have been on the water for 40 years and say they see many more marine mammals now than before.

“Some people are still blown away,” she said.

Data from the DolphinWatch app can help predict when mammals will arrive in the summer in the Chesapeake. In recent years, they started appearing in April and mostly disappeared by October. The numbers seem to peak in July. The diagrams show that dolphins only visit the upper bay in mid-summer.

But their population dynamics and travel patterns are incredibly complex.

Researchers observe dolphins in the Potomac

Researchers Ann-Marie Jacoby (far left) and Janet Mann (far right) observe and photograph dolphins near the mouth of the Potomac River. (Photograph taken under NMFS Permit #19403 by Madison Miketa)

The dolphins that visit the Chesapeake hail from mid-Atlantic waters, from Florida to New York. Some travel further than others. Distinct groups that reside along the coasts of various states generally stay together during their visits, but they also overlap in ways that make it difficult to track movement patterns across the system.

“The marine environment doesn’t have the same barriers as terrestrial populations, so there can be a lot of mixing between groups,” Jacoby said.

This is one of the reasons Potomac researchers wanted to study dolphins here. The Chesapeake is a hotbed of dolphin feeding and social behaviors and a great place to study both. The researchers who have identified, counted and followed them for several years say they have now laid the necessary foundations for further work.

Melissa Collier, a doctoral student at Georgetown and a field researcher at the Chesapeake-Potomac Dolphin Project, studies disease transmission in dolphins. In 2013, in what scientists call an unusual mortality event, nearly 1,600 dolphins washed up along the East Coast, nearly all of them killed by respiratory disease.

Virginia beaches were the epicenter of this outbreak, with more than 400 dolphins stranded, most of them fatally. Necropsies revealed that the deaths were largely from cetacean morbillivirus, a virus from the same family as measles. Collier and other researchers want to better understand how animals that spend most of their time underwater share a virus that is transmitted when they breathe, the same way COVID-19 spreads among humans.

“The thought process is that an epidemic occurs and the natural immunity spreads to the population,” Collier said. “So it goes out and no individual can be infected.”

That is, until new generations are born without immunity, she said. The previous outbreak was in 1987, leading researchers to speculate that, if the quarter-century cycle continues, another could occur in the late 2030s. ask whether human disturbances, such as water pollution, could reduce dolphin immunity over time, making them more susceptible to disease.

To study dolphin behaviors, including those that could spread disease, researchers perform “focal tracking” on a particular dolphin or group. They write if the animals seem to be feeding, mating and surfacing at the same time.

While tracking dolphins this way, Collier, Jacoby and another researcher were part of a team that witnessed the first birth of dolphins in the Potomac River in 2019. Bottlenose dolphins are among the most studied species in the world. world, but a wild birth has only been documented in the scientific literature once, in 2013 off the coast of Georgia.

The birth of the Potomac supports the hypothesis that dolphins come to the bay in summer because it is relatively free of predators, compared to the open ocean, and therefore a safer place for hatchlings. Dolphins carry their young for 12 months, so it’s possible that anyone born here was also conceived here. Avoidance of predators could also explain why they seem to swim higher in the bay than before.

And there are probably other factors – more food and less competition, for starters. Or it could be simple wanderlust, Collier said. “[Maybe] they just want to explore more habitat.

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