In this April 10, 2008, file photo, a North Atlantic right whale dives in Cape Cod Bay near Provincetown, Massachusetts. The right whale population has continued to decline. Credit: Stephan Savoia | AP

The population of North Atlantic right whales is dropping, despite U.S. efforts to protect the critically endangered species from fishing gear and ships.

Fewer than 458 of the whales remain in the waters off the East Coast and Atlantic Canada, down from 482 in 2010, according to a new estimate by researchers with NOAA and the New England Aquarium. That 458 figure is from 2015 and thus does not count 14 deaths this summer, the biggest right whale die-off that researchers can recall.

Those recent deaths, 11 of them off Canada in the Gulf of St. Lawrence, were especially troubling, according to Scott Kraus, a leading right whale researcher with New England Aquarium.

“Probably the last time we saw this level of mortality with right whales was in the 1730s,” Kraus said. Back then, New England whalers were killing a couple of dozen right whales every year.

The latest population decline is worrisome to Maine lobstermen, who already have been required to switch to more-expensive equipment and gear configurations to try to reduce whale entanglements. The lobstermen fear they could eventually be hit with more stringent regulations that would cut further into their profits.

“We’ve got to be worried,” said David Cousens, president of Maine Lobstermen’s Association. “We’re probably going to pay for [the whale deaths] at some point.”

NOAA says additional safeguard measures might be considered within the whales’ known habitat, which stretches from northern Florida to eastern Canada.

“Step 1 begins with learning what we can from the Gulf of St. Lawrence [deaths],” said Michael Asaro of NOAA’s protected resources division in Gloucester, Massachusetts.

Researchers had estimated that from 1990 to 2010, the number of right whales had increased by more than 78 percent — from 270 to 482.

The new population estimate of 458 animals is a result of a new way of tallying them.

Counting them by eye during aerial surveys used to be a reliable method, Asaro said, but the whales no longer faithfully show up each summer off Cape Cod or in the Bay of Fundy.

The new method, which relies more on probability statistics than on visual surveys, is considered more accurate, he said.

The findings of the latest population estimate were published last week in the scientific journal Ecology and Evolution.

Kraus said researchers have been confident for several years that the number of right whales has been declining despite mandates that fishermen reduce the amount of rope on their gear that rises up from the ocean floor. In the past decade, rules for large ships also have been issued to try to prevent whales from being struck.

Kraus said that some of the trends behind the population decline are perplexing. Adult female right whales typically give birth every three years. Yet some 100 female adults produced only five calves this year, an “extraordinarily bad reproduction rate,” he said.

The proportion of females also seems to be declining, perhaps because of females’ tendency to stick closer to shore, where most fishing areas and shipping lanes are, when they are raising young, he said. And there’s evidence that at least some of the whales are getting thinner, which could mean they are finding less plankton to eat.

Patrice McCarron, executive director of Maine Lobstermen’s Association, said her organization is trying to get an independent assessment of the new model’s accuracy but does not dispute that the whales’ numbers are shrinking.

“This is really not going the way we want it to go,” she said. “We’ve all put in a lot of time and effort. And here we are scratching our heads.”

Regulators should investigate how big a role environmental factors, such as food scarcity, might be playing in the whales’ reproduction and survival rates, McCarron said. In the case of the Gulf of St. Lawrence, where the whales may have been pursuing plankton, regulators and Canadian fishermen should consider U.S.-style restrictions on the use of float rope, she said.

“It’s been jaw-dropping to follow,” McCarron said of reports of the dead whales in Canada.

Kraus said there may be some room for optimism. The lifespan of right whales can be 100 years. And females can stay reproductive for several decades, so the population might be able to rebound.

“There’s a lot of resilience there,” Kraus said. “They live a very long time.”

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Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....