Dolphins more common in Potomac than previously thought
Georgetown prof’s marine mammal study could be a boon for river’s cleanup efforts
- Comments are closed for this article.
A waterfront house on Virginia’s Northern Neck promised to be a getaway for Janet Mann from three decades of studying dolphins, primarily in Australia’s Shark Bay.
But the day after Mann and her husband closed on the place in Ophelia, VA, four years ago, she spied an all-too-familiar sight from the shore where the Potomac River joins the Chesapeake Bay.
“I said, ‘Oh, look, dolphins!’ And then I thought, ‘Oh, no,’” Mann recalled. “I think we’ve given up on getting me away from my work.”
A professor of biology and psychology at Georgetown University in the District of Columbia, Mann has since embraced the Potomac as the next frontier for her research. In fact, she’s turned that riverfront retreat into a field station for observing a surprising number of bottlenose dolphins that venture up the Bay’s second largest tributary every summer.
Though dolphins have been spotted occasionally in the Potomac for at least the last six years, Mann said she hasn’t met anyone outside of those who live near her summer house who realize how many of the marine mammals are visiting on a regular basis. Last year, she and her research team of students and other Georgetown faculty tallied nearly 200 different animals in just a two-week span.
“Most people are just shocked,” she said.
Now in its second year, Mann’s Potomac-Chesapeake Dolphin Project is underwritten by the Campbell Foundation; West Marine, the boating retailer, and Georgetown, where Mann is also vice provost for research.
While Atlantic bottlenose dolphins frequent the Lower and Middle Chesapeake Bay and the southern coastline of Virginia in the summer, they’re not often seen venturing into the Bay’s rivers.
Just this month, though, residents of Anne Arundel County reported seeing dolphins for the first time in years in several Upper Western Shore rivers, including the West, Rhode, South and Severn. John Page Williams, a senior naturalist at the Chesapeake Bay Foundation, said he spotted a half-dozen dolphins playing near Hillsmere Shores on July 12 — a sight he hasn’t seen in a couple decades.
“I think it’s a good sign,” he said.
According to historical accounts, dolphins were spotted far up the Potomac in 1884, by the Aqueduct Bridge, just south of Georgetown University. They were an exotic enough sight that, according to reports at the time, men pursued the creatures by boat and tried to shoot or capture them.
In Florida, dolphins are known to go as far as 75 miles up the St. Johns River. But there has not been much Bay-specific research into the species, said Susan Barco, research coordinator at the Virginia Aquarium & Marine Science Center in Virginia Beach.
In a 1998 study for the Virginia Natural History Society, Barco documented dolphin sightings in the Elizabeth River in Norfolk and in the Rappahannock River south of the Potomac. In Maryland, they’ve been reported as far north as Havre de Grace, at the mouth of the Susquehanna River.
The dolphins seen in the Potomac are likely just passing through as they hunt for food, Mann said. Her research project is seeking to answer some basic questions about them: How many are there and where are they?
Mann said her team’s tally in two weeks last July of 193 males, females and juveniles — almost entirely in shallow waters near the river’s mouth — was “extremely high.” In comparison, she wrote on the project’s website, she would expect to find just half that number with a similar survey of Shark Bay, which is thought to have one of the highest densities of bottlenose dolphins in the world.
The total number of dolphins in the Bay and its tributaries is still unknown, but they are likely members of one of several mid-Atlantic groups. The northern migratory coastal stock, which in summer ranges from Virginia to New Jersey, is estimated to number about 11,500, according to aerial surveys by the National Marine Fisheries Service. The Bay waters could also see some overlap in population from a southern migratory group of dolphins, the surveys indicate.
Mann’s team observed dolphins near and in the Potomac River from July to October last year. This year, they started looking at the end of April and counted three on the first day, and then none in May.
In early June, Mann was leisurely kayaking on a Sunday morning when she spotted about 50 dolphins swimming nearby — but she didn’t have her camera to identify them.
The team names the animals they are able to photograph after prominent political figures, past and present; there’s an “Obama,” a “Nixon,” a “Cheney” and several named after founding fathers. Females have been named after the wives and daughters of presidents, vice presidents and congressional leaders.
“We’re starting to run out of names, so we might have to go to speakers of the House,” Mann said. “We thought [the names] might motivate them to get interested in protecting the animals. Like, ‘Oh, I’ve got a dolphin in the Potomac named after me.’”
The photos taken by the team are used to compare markings on the dolphins’ fins and faces with a mid-Atlantic catalog of such images created by Duke University in North Carolina. If the Potomac animals match any of those photographed elsewhere, researchers will know more about their migratory patterns and social structures.
“Do these guys go to North Carolina or Georgia? Are the same individuals returning year to year?” Mann asked, ticking off some of her big questions. She has a hunch, and some anecdotal evidence, that the same dolphins return each year.
“Each month, we know more and are able to match up more animals,” she said.
The team also wants to know how far the animals venture up the Potomac, which they hope to learn by direct observation and interviewing people who live and work along the river.
A 2002 article in The (Fredericksburg, VA) Free-Lance Star quoted two fishermen who said they saw five dolphins in the river’s Monroe Bay south of Colonial Beach that year.
“There will be some point along the Potomac where people will start to say, “Oh, yeah, we used to see dolphins here, but we don’t anymore,’” Mann said.
The summer of 2013 brought a spike in reports of dead dolphins washing up all along the Atlantic coast, the worst die-off since the 1980s. Almost 400 deaths were reported in Virginia that year, compared with 60 in a normal year.
Barco, who responds to dolphin deaths and strandings in Virginia, said the die-off has been linked to a disease, Cetacean morbillivirus, which affects dolphins, porpoises and whales and is in the same family of viruses that causes measles in people. The virus lowers a marine mammal’s immunity, she said, so even if it survives the initial bout, it becomes susceptible to contaminants and other diseases.
“It scared people and made them aware that the health of the Bay could have something to do with the health of these animals,” Barco said.
Better understanding how dolphins behave, mate, feed and socialize in the Bay could help researchers develop treatments for the disease, which has not been known to spread to humans.
Barco said one of the most interesting aspects of Mann’s work will be her ability to compare the local dolphin population with that of Shark Bay, which she has studied for 30 years.
The Australian bay, while as full as the name implies of the sharks that occasionally prey on dolphins, is a comparatively pristine environment for them. Similar work has been done to compare populations of right whales living in the Atlantic Ocean off the East Coast with those living in the Pacific Ocean near Australia and New Zealand, where the animals appear to be healthier.
The dolphins in the Chesapeake Bay migrate here in the summer, while some groups of mid-Atlantic dolphins stay in the same regions year-round.
Already, Mann has noticed that the residential Australian dolphins she’s studied are relaxed, swimming at a slower pace compared with the Potomac ones, who seem to be on a more frenzied search for food. The local populations seem a lot more stressed and constantly on the move, Mann said, though they have observed some playful behavior among the dolphins.
Mann doesn’t yet know what they eat in the Potomac, but most likely it’s a mix of bluefish, croakers, menhaden “and whatever else they can get.”
They do appear to be having calves and, therefore, mating in or near the Potomac, she said. Dolphins have 12-month pregnancies, and they typically birth the calves in the same areas where they mated the year before.
Far more research is needed on the Potomac dolphins before they’ll be as well understood as their Shark Bay relatives, Mann said. But she is already hypothesizing about their impact on the river — and on the public.
The Bay has crabs and oysters and other fish worth rooting for (and eating). But what if Flipper’s relatives could be counted as locals, or at least frequent visitors? Such “charismatic megafauna” are real crowd pleasers and have been used to drive conservation campaigns elsewhere. Perhaps, Mann suggested, their presence in the Potomac could provide fresh fuel for environmental restoration efforts in this region.
“We think it’s a good way to get people interested in protecting the Potomac and the Chesapeake,” she said. “Maybe dolphins will come farther up the river if it’s cleaner.”
- Category: Wildlife + Habitat
By submitting a comment, you are consenting to these Rules of Conduct. Thank you for your civil participation. Please note: reader comments do not represent the position of Chesapeake Media Service.
Comments are now closed for this article. Comments are accepted for 60 days after publication.