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A gray whale was spotted off the coast of New England last week, marking a rare sighting for a species that has been locally extinct in Atlantic waters for centuries.

It was spotted by a team of scientists with the New England Aquarium.

The whale was seen repeatedly diving and resurfacing, apparently searching for food, the aquarium said.

Scientists who spotted the animal say they were in disbelief over the sighting.

"I didn't want to say out loud what it was, because it seemed crazy," said Orla O'Brien, an associate research scientist at the aquarium who was part of the aerial survey team that saw the marine mammal on 1 March.

The whale was spotted 30 miles (48km) south of Nantucket, Massachusetts. Ms O'Brien took photos of it, which she showed to research technician Kate Laemmle, who was also on the plane.

"My brain was trying to process what I was seeing, because this animal was something that should not really exist in these waters," said Ms Laemmle.

According to the New England Aquarium, gray whales are easy to spot due to their lack of a dorsal fin, as well as their mottled grey and white skin.

While they are a common sighting in the North Pacific Ocean, these whales are locally extinct in Atlantic waters, where they have not been spotted since the 18th Century.

But in the last 15 years, there have been five documented observations of gray whales in Atlantic and Mediterranean waters.

Scientists say the reasons behind these sightings are tied to climate change.

Rising global temperatures has meant that the Northwest Passage - which connects the Atlantic and Pacific through Arctic waters - has been ice-free during the summer.

This has meant gray whales have been able to travel between the oceans more freely than in previous centuries.

"These sightings of gray whales in the Atlantic serve as a reminder of how quickly marine species respond to climate change, given the chance," said Ms O'Brien.

This particular whale may have been in Atlantic waters for a few months, the scientists say, as they believe it has been spotted before off the coast of Florida in December.

Other recent unusual gray whale sightings include one off the coast of Namibia in 2015. Four years before that, another was spotted off the coast of Israel.

Researchers at the time similarly linked the rare sightings to warming ocean waters.

"I don't expect that we'll see a brand new population of gray whales in the Atlantic anytime in the very near future," Liz Alter, a biology professor at the California State University in Monterey Bay,

"But it shouldn't surprise us if we start to see a steady trickle of gray whales arriving in the Atlantic."