What dolphins in Chesapeake tell us — and don’t
Though they have big brains, the Atlantic bottlenose dolphins that visit the Chesapeake Bay cannot be expected to have the capacity to read a report card. They have no way of knowing the waters they’ve been cruising all summer received a D+ grade last semester.
“Efforts to restore the bay are struggling to reduce agricultural pollution,” the Chesapeake Bay Foundation said in its annual report card in January. “Urban and suburban polluted runoff is increasing amid inconsistent enforcement by government agencies, new development and climate change.”
If the dolphins spotted as far north as the Elk River, near the top of the bay, could read that assessment, they might not stick around.
But, based on citizen reports to the University of Maryland’s Chesapeake Dolphin Watch, there are significant numbers of dolphins visiting the bay and its tributaries — an estimated 2,000 of them in the lower Potomac River alone. So there must be something good happening out there.
Could the bay be healthier than we think?
Or are the dolphins here because the water quality and food sources are worse elsewhere?
“We don’t know yet,” Ann-Marie Jacoby, associate director of the Potomac-Chesapeake Dolphin Project, told me recently, invoking the scientist’s wise
caution that more research is needed before we fully understand the dolphin presence in the bay.
“It’s hard to know if their population is increasing or decreasing or staying stable when we only have about seven years of data collection on them,” says Jacoby, who has been working on the project since its inception in 2017.
The estimate of 2,000 dolphins in the project’s research area comes from software that identifies individual dolphins based on photographs of their dorsal fins. The photo-matching also helps the Potomac research team track the dolphins’ movement along the East Coast.
Sightings around Baltimore and further north, into the Susquehanna River, are likely due to dry,
hot weather. The less rain the region receives, the higher the salinity of bay water. As temperatures rise, boaters and those who work on the water are likely to see more dolphins, and more of them further up the bay.
Reports to the Chesapeake Dolphin Watch put dolphins in the central part of Maryland’s share of the Chesapeake, between Annapolis and Kent Island.
A Sun reader, Paul Converse, reported seeing dolphins while he was kayaking with friends in the Wye River in early July, upstream of Bennett Point Landing in Queen Anne’s County. “I had taken a diversion to snap a photo of a good-looking osprey,” he says. “I turned around and saw a fin emerging from the water and then a number of
them jumping up.”
A friend who keeps a boat in the Little Choptank River has seen groups of dolphins playing and feeding for up to 45 minutes before losing sight of them.
Further south and on the west side of the bay, dolphins have been reported at several spots in the Patuxent River. They have become a common sight in the Potomac, downstream of the Harry W. Nice Memorial Bridge, on Route 301 in Charles County, though some have been reported further upstream and closer to the nation’s capital.
“We see mating behaviors in the summer months and gestation is about 12 months for dolphins,” Jacoby says. “So, we think that the dolphins we’ve seen across multiple years are breeding
and birthing in the Potomac. We also see quite a few newborns throughout the summer.”
Dolphins appear to move out of the bay as the water temperature drops, Jacoby says. That’s borne out by readings from battery-powered listening devices deployed in waters where dolphins vacation during the summer.
So why do we want to know all this?
Dolphin research is not an academic exercise.
In the early 1970s, Democratic majorities in Congress gave us the Clean Air Act, the Clean Water Act and, among other progressive laws, the Marine Mammal Protection Act. The latter called for the protection of all marine mammals and the management of their stocks in U.S. waters.
That requires data, and federal agencies responsible for dolphins, whales and other mammals — NOAA Fisheries and the U.S. Fish & Wildlife Service — had little to none about dolphins in the Chesapeake.
Jacoby’s work on the Potomac project includes interviews with watermen and the mining of newspaper archives. She has pretty much established that dolphins have been visiting the nation’s largest estuary for a long time.
Maybe a very long time. In fact, for those awed by the sight of dolphins in the bay and wondering about their history here, something of an answer emerged from the beach along fossilrich Calvert Cliffs on the first Saturday of August.
A woman discovered a nearly complete fossilized skull of a sea creature. It was about two and half feet long and weighed about 50 pounds. Experts at the Calvert Marine Museum in Solomons identified it as the skull of a dolphin-like marine mammal from 12 million to 20 million years ago. Stephen Godfrey, the museum’s curator of paleontology, says “the most diverse assemblage of dolphins known anywhere on Earth” lived in the ancient ocean that once covered the region.
So you might say today’s bottlenose dolphins swim where their Miocene ancestors once did.
Is it possible that dolphins know this? Is it possible that some tiny grain of prehistoric memory buried deep inside their ample brains could spark the instinct to return to waters where their ancestors once cruised? As Ann-Marie Jacoby says,
“We don’t know yet.”