Maryland Natural Resources PoliceSgt. John Buchanan was flying biologists over Tangier Sound this spring to survey ducks when he glimpsed gray bodies arcing in the waters below.

The veteran pilotlowered the helicopter for a closer look.

Two, three, four pods of dolphins. He counted almost 50 of the mammals in the lower Chesapeake Bay.

“One of the largest groups that I’ve seen,” Buchanan said. “Over the last few years it’s not uncommon to see them.”

Now researchers in Maryland and Virginia are undertaking the first comprehensive studies of bottlenose dolphins in the Chesapeake Bay. Their early findings suggest more dolphins are swimming up into the bay — they have been spotted as far north as Annapolis and the Bay Bridge — than previously believed.

“We may have well over 1,000 dolphins coming into the bay, which is far more than I think anyone expected,” said Helen Bailey, a research professor with the University of Maryland Center for Environmental Science.

When Baileydropped an underwater microphone off the pier at the Chesapeake Biological Laboratory on Solomons Island last June, she heard dolphin squeaks, clacks and whistles. As the mammalscruised past, she wondered: Where are they going?

Bailey hopes for clues with the release this month of a new cellphone app that will enable bay users to report dolphin sightings. Her DolphinWatch app will mark locations, dates and times of sightings and plot them on a map of the bay.

Bailey plans to use the data to determine where to deploy more underwater microphones. One device has recorded dolphins near the mouth of the Potomac River every day for the past two weeks.

“They’re obviously going somewhere to feed, and I don’t think it’s at the mouth,” she said. “I just don’t know where it is.”

Bottlenose dolphins can grow to 12 feet long, weigh 1,400 pounds and swim 22 mph. The females may live half a century. Sightings start in April and end in October.

Acrobatic and clever, dolphins live in all butthe coldest ocean waters — in different places they develop different behaviors. Those near Hawaii earned the name “spinners” for their aerial pirouettes. Off the Florida Keys, they’ve learned to churn up the sea floor and corral prey with mud plumes. On the floor of Shark Bay, Australia,they don sea sponges to guard their snouts when foraging.

And the Chesapeake dolphins?

“We know almost nothing,” said Eric Patterson, a biologist with the National Oceanic and Atmospheric Administration. “We don’t even really know what population or stock they belong to.”

A handful of distinct populations swim along the East Coast in a migration route that extends from New York to Florida. Together, NOAA researchers estimate,these groups exceed 14,000 dolphins.

Biologists suspect some of the dolphins — perhaps enticed by rockfish and croaker — have taken to summering in the Chesapeake Bay. They don’t know if the gray guests have a taste for blue crabs.

“We think it is actually a really important feeding area,” said Janet Mann, a biology professor at Georgetown University. “They’re getting pregnant here and they’re having babies here.”

In fact, researchers have found denser pods in the lower Chesapeake than off Western Australia, Patterson said.

The growing awareness of Chesapeake Bay dolphins began by happenstance.

Mann and her husband bought a cottage five years ago on the Potomac and discovered their new aquatic neighbors. She bought an 18-foot boat and began taking pictures.

She has identified more than 500 dolphins around the mouth of the Potomac in the past two summers. She names them after presidents, first ladies, Founding Fathers, even Supreme Court justices. Her first was Benjamin Franklin; she named a mother and calf Barbara and Jeb Bush.

Mann calls it the Potomac-Chesapeake Dolphin Project. She photographs the mammals’ dorsal fins, distinct as fingerprints, with various nicks, scars and coloring, and sends the images to Duke University, which maintains a database with thousands of such photos.

About a third of the dolphins she identified in 2015 returned the next summer.

Bailey, hired by state and federal officials last year to study the waters off Ocean City where developers want to erect wind turbines, placed underwater microphones and published her results last month.

She reported dolphins visit the two sites proposed for the turbines mostly in winter and spring, and recommended construction of the turbines be delayed until summer to reducethe impact on dolphins.

Baileypartnered with Mann and placed a microphone in the Potomac. As their research progressed, they heard more and more dolphin tales.

“Either people are more aware, or there are more dolphins,” Mann said.

Bailey wonders if some condition is changing behavior of dolphins migrating along the Atlantic Coast.

“One of the problems is a lot of the information is anecdotal,” she said.“We’re only just starting to systematically report sightings.

“We’re probably seeing an increase, and it may have to do with changes in the water.”

Brent Whitaker tracks wildlife data at the National Aquarium in Baltimore. He says the bay is growing increasingly temperate.

“We’re seeing seals coming down farther south and dolphins coming up from the south,” he said. “As water temperature changes and food stocks move, I think that’s why we’re seeing changes in the animals.”

Occasional dolphin sightingsin the bay have been reported for centuries. An 1800s account tells of one dolphin swimming up the Potomac to Washington. There have been recent sightings as far upriver as the Gov. Harry W. Nice Memorial Bridge, which carries Route 301 over the Potomac from Charles County to Virginia.

Buchanan, the pilot, says he has seen dolphins near Kent Island and in the Choptank and Miles rivers on the Eastern Shore. Anne Arundel County families were surprised last July when dolphins swam through the Severn, South, West and Rhode rivers. Some two dozen were glimpsed off the Naval Academy sea wall in Annapolis.

Amanda Weschler investigates dead dolphins and sea turtles for the Maryland Department of Natural Resources. She saysshe’s heard of dolphins spotted north of the Bay Bridge near Pasadena.

“The general public is not aware of the number that we see every year,” she said.

Chesapeake dolphins drew attention four years ago when the carcasses of nearly 80 washed up on Maryland shores. Dolphins were found with lesions on their skin, mouths and lungs around the Atlantic Coast. NOAA investigators counted about 1,800 deaths between 2013 and 2015, six times more than the previous five years combined. They suspect a contagious virus similar to measles.

Bailey and Mann aim to understand such threats while solving the lingering mysteries of the Chesapeake dolphins. Graduate student Ann-Marie Jacoby studied with Mann at Georgetown. She plans to begin her own project traveling along the Potomac to collect accounts of dolphin sightings.

“Nobody has really studied the dolphins until now,” Jacoby said. “There’s a ton of questions that can be answered, which is really exciting.”

Bailey plans to launch theDolphinWatch app in the last week of June. She is raising money for 10 more battery-powered hydrophones — each costs about $3,000 — to deploy across the bay. And Mann will continue photographing dolphins this summer. Both hope to publish their results.

tprudente@baltsun.com