A group of 17 North Atlantic right whales was spotted by an aerial survey team 21 miles south of Nantucket early this week, prompting a renewed call for voluntary speed restrictions among mariners and also renewed concern for the future of the critically endangered mammals.

In response to the whale sighting early Monday, the National Oceanic and Atmospheric Administration (NOAA) has instituted a voluntary vessel speed restriction zone, also known as a DMA, or dynamic management area, that encompasses Nantucket and extends to the southeastern coast of Martha’s Vineyard and Chappaquiddick. Boaters are asked to limit their speed to 10 knots or less when sailing through the area, which spans latitudinally from 40 degrees, 28 minutes north to 41 degrees, 22 minutes north, and longitudinally from 70 degrees, 39 minutes west to 69 degrees, 29 minutes west. Overall, the rectangular area encompasses approximately 360 square nautical miles.

With only about 400 whales remaining, the North Atlantic right whale is one of the rarest marine mammals in the world. The whales are known to appear around Cape Cod and the Islands around this time of year, fattening up on zooplankton before heading south to breed. Two weeks ago, NOAA reported a sighting of four right whales in a similar location off Nantucket’s south shore. But 17 is an entirely different story.

Two right whales photographed by aerial survey team. — NOAA/NEFSC/Leah Crowe Permit # 21371

“That’s a lot of whales,” said Jennifer Goebel, a spokesman for NOAA, speaking to the Gazette Tuesday. “Usually when we set up these dynamic management areas we can do it on anything over three, sometimes four, maybe five. This was 17, so that tells you.”

Although aggressive conservation efforts to preserve the right whales raised the population from historic lows in the late 1980s to a peak of over 500 in 2010, the past decade has seen a plateau, and most recently, a drop in the population. Just as zero calves were spotted during the 2017 and 2018 breeding season, an unprecedented 20 adult whales were reported dead in the same year, causing NOAA to declare an “unusual mortality event” and sparking fear among scientists that the species is teetering on the brink of extinction.

A study published earlier this month, led by Peter Corkeron,an endangered species expert from the NOAA Northeast Fisheries Science Center, concluded that the slow growth in the North Atlantic right whale population, compared with the much more rapid recovery of its counterpart the Southern right whale, is due to anthropogenic (human) rather than intrinsic causes.

North Atlantic right whales are at severe risk of entanglement from fishing ropes. According to the study, almost all individual North Atlantic right whales have been entangled at least once (83 per cent), and more than half have been entangled two or more times (59 per cent). Of all the ocean’s right whale species, the North Atlantic also has the most heavily industrialized habitat.

“Compare the southern coast of Australia or South Africa with the East Coast of the U.S./Canada,” Mr. Corkeron said in an email to the Gazette. “Where North Atlantic right whales occur has far more human activities in it than southern rights’ habitats do.”

According to the study, zooplankton productivity has not decreased to the extent that it could be the sole reason for the right whale’s poor calving record, furthering the hypothesis that the decline in right whale calves is anthropogenic. A 2016 study, using visual assessments, determined that the overall body condition of the North Atlantic right whale had declined in conjunction with the decline in calf counts.

“That female baleen whales forgo reproduction in response to poor body condition is well established,”the study says. “The energetic demand from the drag associated with entanglement can be comparable to the cost of a one-way migration, and is sufficient to impact the likelihood that a female can successfully reproduce.”

While the North Atlantic right whale calf counts increased at 1.98 per cent from 1992 to 2016, its counterpart in less heavily-fished waters, the Southern right whale, increased at 5.34 per cent. With all else being equal, the study said the North Atlantic population should have increased at approximately 4 per cent every year from 1990 to 2016.

“Had North Atlantic right whales increased at the annual rate at which they are capable,” the study found, “the species’ numbers would be almost double what they are now, and their current emergency wouldn’t be so dire.”

For Mr. Corkeron, who has devoted himself to the whale conservation for much of his professional life, the study quantified a troubling phenomenon of which he was already well-aware.

“The results weren’t particularly surprising,” he wrote. “But they needed to be demonstrated clearly.”

The right whales spotted south of Nantucket are moving south for the winter, where they will hopefully bear young in the warmer waters off the Gulf of Mexico and Florida coast. An advisory from NOAA cautions mariners to give the whales room as they migrate, and asks commercial fishermen to be vigilant when maneuvering to avoid accidental collisions, remove unused gear from the ocean, and use vertical lines with required markings, weak links and breaking strengths.

Even though the 17 whales were spotted by the science center’s aerial survey team, NOAA also asks mariners to contact the whale hotline at 866-755-6522 if they see any out on the water.

Meanwhile, scientists are awaiting the winter with nervous anticipation, both cautious and optimistic about what the future holds for the North Atlantic right whale.

According to Mr. Corkeron and NOAA spokesperson Ms. Goebel, guessing calf numbers is difficult, meaning that there could be anything from zero (a bad year), to 20 (a good year). Although seeing 20 would be unlikely, they are holding out hope for more than zero this winter.

“There weren’t any last year, but we’re hoping to see some calves come January,” Ms. Goebel said. “Fingers crossed.”