There has not been a single North Atlantic right whale calf spotted this year, an unprecedented and alarming sign for this critically endangered species.

Scientists expect to see mothers and calves making their way north toward Atlantic Canada by the end of February. But halfway through March, there hasn't been a single calf sighted.

In fact, this is the first year no calves have been spotted by the end of February.

"I've been working with right whales to one extent or another since the late '80s, early '90s and I have to say I have not been this concerned," said Barb Zoodsma, right whale biologist with the National Oceanic and Atmospheric Administration.

She said breeding-age females are the first to reach breeding grounds in the winter off Florida and Georgia and they're also the first to start making their way back to summer feeding grounds off the U.S. Eastern Seaboard and Atlantic Canada.

"The critical information is that this is the only known calving area for North Atlantic right whales. We fly our aerial surveys for the purpose of detecting calves that the right whales are producing and this year we haven't seen any calves at all," she said.

Zoodsma said the aerial surveys have even been expanded into the Gulf of Mexico this year for the first time. But no luck.

Lack of calves 'does not bode well' for species

Philip Hamilton, research scientist for the Anderson Cabot Center for Ocean Life at the New England Aquarium in Boston, said aerial surveys will end in the next few weeks.

"There is always a chance they will find something, but the overall lack of whales in the southeast does not bode well," he said in an email.

Last year, three calves were seen in the calving area and an additional two were spotted elsewhere — one in Cape Cod Bay the other in the Great South Channel, a deep-water passage between Nantucket and Georges Bank.

A Skymaster whale survey plane looks for North Atlantic right whales in Cape Cod, Mass. (Center for Coastal Studies)

Hamilton said there's still a chance of seeing a calf in the feeding grounds this spring and summer, but it's not looking good.

But Zoodsma said the lack of calves this year is further evidence things are not well in the population, which is estimated to be just 450.

In the last year, at least 18 dead right whales have been found — 12 in Canadian waters and six in U.S. waters. Scientists believe human activity, including shipping and fishing, was the primary cause. The most recent carcass was found Jan. 25.

Why are females dying so young?

Also of concern is the fact that North Atlantic right whales don't live as long as one would expect, based on whales of similar size.

"We look to the longest-lived right whale that we know of and that was about 75 years old and we also look to other species that they're closely related to. Bowhead whales can live to be 100 or 200 years old," said Zoodsma.

But right whale females, on average, are only living to be between 20 and 30 years old and usually produce their first calf when they're about 10 years old.

A right whale feeds just below the surface of Cape Cod Bay in April 2017. (Center for Coastal Studies/NOAA permit #19315/AP)

Healthy, reproductively active females should produce a calf every three years. But Zoodsma said the five mothers who gave birth last year have a calving interval of seven years.

"So not only are the females not living very long, they're having fewer calves for whatever reason," said Zoodsma. "To me that's a huge red flag. It suggests that something is awry with these females."

Though it's not known why females in particular are doing poorly, scientists do know that ship strikes and fishing gear entanglements are a big problem for right whales.

Amy Knowlton, a scientist at the New England Aquarium, said at a right whale meeting last fall 85 per cent of all right whales have been entangled in fishing gear — and 50 per cent have been entangled more than once.

She said females are also more negatively impacted by entanglement.

With only about 100 breeding females in the population, Zoodsma said "things can turn south in a very big hurry and so we really need to get serious in finding solutions."

Earlier this year, Fisheries and Oceans Minister Dominic LeBlanc announced changes to the snow crab fishery to reduce the number of entanglements.

Last summer, Transport Canada imposed a mandatory 10-knot speed limit in the western part of the Gulf of St. Lawrence for vessels 20 metres or longer to help reduce the risk of whale strikes and to improve the chances of survival for any whales that are struck. It's not clear whether that speed restriction will be imposed again this summer.