Rescuers may have to free the whale, she added in a statement Friday.
“The naturalists onboard the New England Aquarium Whale Watch in partnership with Boston Harbor City Cruises, reported it to the Center for Coastal Studies Disentanglement team in Provincetown,” Green said.
Laura Lilly, a naturalist with the aquarium and the cruise company, said in a phone interview Friday afternoon that it was unclear if the whale remained trapped in the fishing line.
She said about 70 percent “of the whales in this area become entangled at least once in their lives.” She said anyone who sees an entangled whale can report it by calling a hotline at 800-900-3622, or by hailing the Coast Guard on VHF radio channel 16, Lilly said.
Green said entanglements are common in areas with high recreational boater activity; some 70 recreational boats were spotted around the whale in the harbor one day this week, Green said.
“It is helpful, when people are fishing, and they see a whale nearby, that they pull their lines out of the water until the whale moves on from the area,” Green said. “It is very special to see such a majestic mammal in its natural habitat, but it is important to give the whale space to move freely.”
In aprila North Atlantic right whale that gave birth in December 2021 while entangled in rope was spotted with her calf in the waters off Cape Cod.
More recently, 56-year-old Joe Fabiano on Monday captured spellbinding video footage while out on his boat of a humpback whale splashing around Boston Harbor.
Lilly said Friday that that was the same humpback that was spotted entangled in fishing line Wednesday, and that researchers can identify the whales based on their tail markings.
Jooke Robbins, director of the Humpback Whale Studies Program at the Provincetown Center for Coastal Studies, said the whale seen entangled Wednesday was probably the same one caught on video earlier in the week, but she could not say for certain Friday night because she didn’ t have access to high-quality images of the animal.
Robbins said entering waters so close to human activity can be hazardous for whales, and for the people near them.
“As we enter the weekend, we strongly recommend that boaters stay vigilant and at least 100 feet away (preferably more) from any whale in these unusual locations,” she said in an e-mail. “Typically, they are young whales that are a bit less experienced and just working hard to find food.”
Fabiano said earlier this week that he was out on the water with Paula Brogna, 55, after launching his boat from Winthrop around 5:15 am Monday. They were waiting for the sun to come up, a time “when the fish get really active,” he said.
Not long into their fishing trip, Fabiano and Brogna heard something that sounded like “a big flipper hitting the water.” But when they looked around there was nothing there — and no boats were close by.
“But you could see the water was white from the splash, so we were like, ‘What was that?,’” said Fabiano. “Next thing you know, she goes, ‘Oh, my God. That’s a whale.’”
Fabiano, who had only ever seen seals or dolphins out on the water before, grabbed his phone and started recording.
This summer’s not the first time humpbacks have been spotted in Boston Harbor.
In 2016the captain of a commuter boat traveling from Boston to Hingham saw a whale swimming just a quarter-mile off the tip of Castle Island. Two years laterseveral whales were captured on video while feeding in the area.
CORRECTION: Because of incorrect information provided to the Globe, an earlier version of this story misstated the day the humpback whale was seen entangled in the fishing line in Boston Harbor. The whale was seen entangled on Wednesday.
Material from prior Globe stories was used in this report. Globe correspond Jeremy C. Fox contributed.