Three common dolphins made an appearance in the Edgartown harbor Monday, delighting onlookers and creating a buzz about the species of the mammalian visitors.

The dolphins were spotted in the harbor beginning early Monday morning and into the afternoon.

Jennifer Marshall from Mystic, Conn., took this photo of all three dolphins.

Jennifer Marshall

Jennifer Marshall from Mystic, Conn., took this photo of all three dolphins.

Jennifer Marshall

Scott Kraus, vice president of research at New England Aquarium and a longtime whale researcher, positively identified the mammals as common dolphins.

New England Aquarium media relations director Tony LaCasse said the color pattern and body size help distinguish the common dolphin from the Atlantic white-sided dolphin. “Both species are the predominant dolphin species in New England waters,” Mr. Lacasse wrote in an email to the Gazette. “They are also the most common stranding candidates, particularly in the winter on Cape Cod.”

Common dolphins are more slender than Atlantic white-side dolphins, and are usually seven to eight-and-a-half feet long and weigh between 200 and 300 pounds. In the summer, most of the common dolphin population moves to deeper water near the continental shelf, or in the center of the Gulf of Maine, he said. They eat fish and squid.

Common dolphins are gregarious and often gather in large groups, from tens to hundreds of dolphins, Mr. LaCasse said. They will also hang out with other dolphin species.

While the local population is thought to be stable, the common dolphin is protected under the Marine Mammal Protection Act.

“Many of your readers have probably seen common dolphins bow-riding off of large vessels like whale watch boats underway,” Mr. LaCasse said.