After a year of rising concern about North Atlantic right whales, which scientists say could go extinct in the next 20 years, researchers have yet to document a single newborn whale during the calving season that is coming to an end.

Bad news about the calving season follows a year with 17 documented unnatural right whale deaths in the United States and Canada, an alarming number for a species with a population of about 450 animals.

Scientists said this week that it’s too early to say with certainty that no calves were born this year, but things are not looking good. The official number won’t be known until around July, according to biologist Peter Corkeron, who leads the large whale team of the protected species branch at NOAA Northeast Fisheries Science Center.

“I don’t want to downplay how bad this is, but we don’t yet know zero,” he told the Gazette this week. “If there were 20 calves born somewhere else, I think we’d know about. While it’s too early yet to say zero, it’s not too early yet to say — well this isn’t looking very good, is it.”

Mark Baumgartner, a biologist with Woods Hole Oceanographic Institution and leader of the North Atlantic Right Whale Consortium, agreed. “It’s not

looking like this is a boom year, that’s for sure,” he said. “If I were to guess I would think it would just be maybe one or two calves. We’re not looking for a stash of 10 calves.”

North Atlantic right whales generally give birth in the winter in the ocean off northern Florida and southern Georgia. Mr. Baumgartner said whales have had calves in the Gulf of Maine “once in a blue moon.”

Aerial surveys over southern waters during calving months are on the lookout for female whales and their calves. Because the whale population is so small, scientists have documented each individual and have a good idea about the number of females who are of calving age and due to give birth. Mr. Baumgartner said historically there has been a three-year interval between when female right whales have calves. As of last year, the average interval was 10 years.

“That’s very distressing,” he said. “Lots of females out there who have gone through their breeding cycle. They are in the waiting stage, resting stage, should have calves, and they’re not.”

Sean Hayes, chief of the NOAA fisheries protected species branch, said the agency’s southern Atlantic staff had seen two female whales of calving age about a week ago, but nothing since then.

And still no calves.

Calves are easy to spot, Mr. Corkeron said, because they stay close to their mothers and right whales tend to swim near shore.

“The level of survey efforts in the southeast is just enormous,” he said. “If they’re down there, we see them.”

He said the low birth rate this season was a logical result of a population that has been decline since 2010. Mr. Corkeron co-authored a scientific paper released last fall documenting the decline of the species, which scientists say is on track to go extinct in about 20 years.

The reason no calves have been found isn’t clear, scientists said this week, though fishing gear entanglement and access to food are likely part of the problem.

Female calves expend an enormous amount of energy to have a calf and then nurse the baby for the better part of a year, Mr. Corkeron said. The females pack on blubber through feeding on tiny crustaceans called copepods in the waters off New England and Canada. Right whales do not feed when they are in southern waters to give birth, so they have to rely on large stores of food to sustain them and produce nutrient-rich milk for their calves.

If the whales don’t get enough food, or if they expend energy through being entangled in fishing gear, they won’t get pregnant, Mr. Corkeron said.

Mr. Baumgartner said right whales seen recently are generally in poor health and too skinny. Whales have had changing movement patterns since 2010, he said, which coincides with the population decline and could indicate they are not finding the food they need, perhaps because of changes to the ecosystem.

“It’s not a great stretch of the imagination that the warming process is affecting small crustaceans that right whales feed on,” he said. “If that really is happening, they’re probably moving around a lot more. If that’s happening they don’t get enough calories on a daily basis, and are doing a lot of work.”

Fishing gear entanglement, which has been identified as the main cause of unnatural whale deaths, is also a factor. When entanglement isn’t fatal, Mr. Baumgartner said, dragging around heavy gear and having open wounds expends fat reserves. “Females that get entangled delay reproduction for many years,” he said.

Scientists like Mr. Baumgartner are working on ways to decrease fishing gear entanglements, including ropeless technology for lobster pots. A Feb. 1 workshop was well-attended by fishermen, scientists, regulators, and conservation groups from the U.S. and Canada, he said, as well as potential funders.

“I will not say that everyone is embracing ropeless technology,” Mr. Baumgartner said, but fishermen are willing to move forward with testing the technology, he said. “It’s on us to work quickly.”

A dip in the number of newborn calves isn’t unprecedented, Mr. Baumgartner said. In the late 1990s there was real concern about a decline in the species, he said, with one calf born in 2000, and relatively small numbers in the years before that. Things turned around in 2001, when 31 calves were born.

This year’s calving season comes along with the high number of deaths, Mr. Baumgartner said, and results in troubling math. In 2017, five calves were born and 17 whales were reported dead.

“The reason we worry about zero a lot really has to do with how many

whales are dying,” he said. There has been one reported right whale death this year, a 10-year-old female found off the coast of Virginia. The preliminary cause of death was entanglement in fishing gear.

“We already have a mortality and have zero calves,” Mr. Baumgartner said. “Already at minus one in the tally sheet for this year. Based on years past, there’s a high likelihood that more right whales will die this year. And that will be just digging ourselves more and more into a hole for this year.”

The 17 well-publicized right whale deaths last year and alarming news about the calving season has brought public attention to the issue, which Mr. Baumgartner called “the only silver lining on a very dark cloud.”

Mr. Corkeron said he has seen the same thing.

“It’s now so bad that everyone has to pay attention,” he said. “Some of us have been hanging on about this problem for years. It hasn’t been bad enough to grab people’s attention. Now it kind of is.”