Two of the dozens of North Atlantic right whales gathered off the coast of Portsmouth, N.H., are seen Sunday. Photo courtesy of New England Aquarium

Dozens of North Atlantic right whales — more than 15% of the estimated global population — are gathered off Jeffreys Ledge, east of Portsmouth, New Hampshire, triggering a slow zone for boaters.

Surveyors at the New England Aquarium spotted at least 70 individual whales grouped in a small area on Sunday, said Orla O’Brien, head of the aerial survey program.

“Our best estimate is that between the two survey days that we flew Sunday and Monday, there’s probably at least 75 unique whales in that area,” O’Brien said. “For these waters, in this time of year, it’s a lot of whales.”

Jeffreys Ledge is a “very productive area for marine life,” so it’s not surprising that it attracted an unusually large number of the critically endangered species, O’Brien said. Historically, smaller groups of right whales have congregated there in the fall, she said.

“They’re not really social animals. They don’t travel around in packs, for instance,” she said. “I think it’s more that they’re being cued in by similar signals. … Maybe there is a part of it where they are hearing other whales or something like that.”

A “large amount” of fixed fishing gear was also spotted in that area, the National Oceanographic and Atmospheric Administration Fisheries said in its announcement.

“Whales were observed in close proximity to the gear, which presents a high risk of entanglement,” the administration said in the announcement. “Please be aware of this aggregation and take every precaution to avoid entangling or colliding with these whales as they feed.”

Mariners are asked to slow to a maximum speed of 10 knots. Following that guidance is voluntary, but knowingly approaching a right whale is illegal.

“Boaters are also reminded that approaching a right whale closer than 500 yards is a violation of federal law,” the administration said.

Jeffreys Point is heavily trafficked by fishermen, O’Brien said, adding that the aquarium requested that the Coast Guard notify mariners about the group.

“When you see stories of a group of 70 whales it’s like ‘Wow this is so exciting,'” O’Brien said. “But I think right now there’s also an overwhelming feeling of nervousness, because there’s been a lot of entanglements recently.”

There are fewer than 400 North Atlantic right whales living in the wild, according to the latest population count, though the population appeared to grow slightly since the previous count in 2020. Boat strikes and fishing gear entanglement are among the most common causes of death for the critically endangered species.

Climate change is contributing to warmer waters in the Gulf of Maine, as well as shifting currents and behavior by species the right whales prey on, O’Brien said. That’s disrupting some traditional migratory and behavioral patterns, and points to the value of continued monitoring, she said.

“In some senses its the new normal, but it doesn’t mean the new normal is Jeffreys Ledge in January,” O’Brien said. “It means they’re popping up in new places.”

But monitoring and establishing slow zones as needed can only do so much and is not always feasible, O’Brien said. She argued that the Jeffreys Ledge sighting highlights the need for regulations that can reduce risks for whales more broadly.

“The whales are showing us that they’re popping up in areas that we’re not ready for them all the time,” O’Brien said.