Dolphins return to Long Island Sound

A pod of about 10 bottlenose dolphins broke the surface of the Long Island Sound this month as marine scientist Allison Rugila and her colleagues watched from a boat near Plum Island.

"It was just lovely to see," said Rugila, who is the western Long Island soundkeeper with the environmental group Save the Sound.

In the past several years, scientists and boaters have reported more frequent sightings of dolphins and in larger pods in the Long Island Sound, from Sands Point to Huntington Bay and Port Jefferson.

"There definitely are more dolphins now than there were a few years ago," she said.

The reasons for those increases are varied, according to Rugila — some are indicators of improved conditions in the Sound, and some are signals of warmer water temperatures.

Atlantic bottlenose dolphins are among the most charismatic of cetacean species, with their acrobatic leaps and their upturned mouths that give them the appearance of a perpetual smile.

The highly social animals hunt communally, using echolocation to track their prey, and they communicate with one another with a complex vocabulary of clicks, chirps, whistles and squeaks. Decades ago, marine biologists studying their vocalizations found that each juvenile dolphin creates a "signature whistle," which functions like a name: they use it to identify themselves to others, and they respond when other pod members call out their distinct whistle.

Once abundant

Dolphins were abundant in the Sound before the 1940s, according to the Long Island Sound Partnership, but in the decades that followed, they seemed to disappear, most likely because of deteriorating water quality and overfishing of dolphins' prey fish, such as menhaden and herring.

Then in June 2009, large numbers of bottlenose dolphins swam up from New York Harbor, into the East River and then into the Sound, according to Art Kopelman, senior scientist and president of the Coastal Research and Education Society of Long Island. Roughly 200 dolphins, including adults, juveniles and young calves, were spotted swimming near Glen Cove and later in Cold Spring Harbor, Oyster Bay, Huntington Bay and around Hempstead Harbor, and later in the summer by Montauk Point.

Since then, Kopelman told Newsday, "there has been a regular summer population on both the North Shore and the South Shore."

Joby Vinarski, a captain with Long Island Fishing Charters, told Newsday he has seen dolphins in the Sound fairly regularly for the past 12 years or so, often in pods of about a dozen. But in the past three or four years, they’ve been "much more prevalent," he said.

In July, he watched from his boat as a pod of at least 50 swam just off Sands Point, repeatedly surfacing and submerging as they fed. "That was just a miraculous number of them," Vinarski said. "And it was a lot of calves too, which is so nice to see."

"While dolphins visiting the Long Island Sound is not new, anecdotal reports this year indicate a more consistent seasonal presence compared to previous years," Samantha Rosen, from the state Department of Environmental Conservation’s marine division, wrote in an email to Newsday. But she said "there has been no targeted research or confirmed causes."

Why the recent uptick?

Ecologists point to several reasons that more dolphins may have been summering in the Sound recently.

One is improved water quality, Rugila said, as high nitrogen levels in some of the Sound’s bays and harbors have decreased because of improved sewage treatment.

The more frequent sightings also may be an effect of global warming. Dolphins, which generally inhabit temperate to tropical waters, seem to be spending more time farther north as the climate and coastal waters heat up, Rugila said. That trend is magnified in the Sound, where in the previous four decades the water has warmed four times faster than in the global oceans, according to a 2019 study from the University of Connecticut.

"We are seeing dramatic shifts in the marine communities that exist in the Long Island Sound because of warming water," Rugila said. There are more blue crabs, which have historically thrived in the Chesapeake Bay; black sea bass, which used to be a seasonal resident, now stay year-round. At the same time, there are far fewer lobsters and winter flounder, which both prefer colder water.

It’s wonderful to see dolphins — "these lovely megafauna" — in the Sound, she acknowledged. "But it's a also symptom that things are not where we want them to be."

The dolphins also are probably chasing good prey in the area. Dolphins are opportunistic feeders, happy to eat whatever fish they find. But recently, Rugila noted, the local river herring population has increased with more careful management, and dolphins seem to be making the most of a newly abundant food source.