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North Atlantic right whales are in far worse condition than other right whales, new study finds

Healthy Southern right whales from three populations (left three photographs), next to a much leaner North Atlantic right whale (right) in visibly poorer body condition.
Healthy Southern right whales from three populations (left three photographs), next to a much leaner North Atlantic right whale (right) in visibly poorer body condition.Photos: Fredrik Christiansen (left & center-left), Stephen M. Dawson (center-right), John W. Durban and Holly Fearnbach (right)

A new study from an international team of researchers has found that North Atlantic right whales are unhealthy and have depleted stores of fat, one of the biggest challenges the species faces in its fight for survival.

Researchers behind the study, which was published in the journal Marine Ecology Progress Series Thursday, said this finding will help shed light on why North Atlantic right whales are so close to extinction.

“We know that North Atlantic right whales as a species are doing poorly, but this work brings home that as individuals, they’re also doing poorly," said Peter Corkeron, a researcher at the New England Aquarium and co-author of the study.

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Corkeron worked with researchers from 12 institutions in five countries to compare the body conditions of North Atlantic and Southern right whales; the study is the largest assessment of baleen whales in the world, according to researchers.

Researchers used drones to photograph numerous North Atlantic right whales and populations of right whales in Argentina, Australia, and New Zealand. The pictures were later mapped together to measure the length and widths of the right whales so researchers could estimate their body volumes.

After creating an index of the whales’ conditions and sizes, researchers found that North Atlantic right whales of all ages weighed less and were in far worse condition than right whales in the Southern Hemisphere.

“Good body condition and abundant fat reserves are crucial for the reproduction of large whales, including right whales, as the animals rely on these energy stores during the breeding season when they are mostly fasting,” said Dr. Fredrik Christiansen, a professor at Aarhus University in Denmark and the study’s lead researcher.

Researchers said poor body conditions could be stunting the growth of juveniles and delaying when they are able to reproduce. It could also explain why so many of these whales are dying or not giving birth.

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“This comparison with their Southern Hemisphere relatives shows that most individual North Atlantic right whales are in much worse condition than they should be,” said Michael Moore, a researcher from the Woods Hole Oceanographic Institution and a co-author of the study.

About 10,000 to 15,000 right whales live in the Southern Hemisphere, with most populations of these whales doing well since commercial whaling largely came to an end in the 20th century, researchers said.

Only 410 or so North Atlantic right whales remain off the east coast of North America.

“Their decline has been so rapid that we know it’s not simply because not enough calves are being born; too many whales are also dying from human-caused injuries,” Corkeron said.

Vessel strikes continue to injure and kill North Atlantic right whales, as do entanglements in lobster and crab pots and other fishing gear, researchers said.

Southern right whales haven’t had the same problem because they live in areas that are far less industrialized.

“Ninety percent of the human species live north of the equator. Thus the consequent densities of vessel traffic and fishing gear deployed is far less," Moore said.

Injuries from vessel strikes and entanglements have weakened many North Atlantic right whales and made them less likely to have a calf, researchers said. The plankton they eat has also moved from the Gulf of Maine to the Gulf of Saint Lawrence due to warming waters in recent years.

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“Baleen whales are memory-based, cultural foragers, so they go to where they’ve found food before,” Moore said. “When food moves, they have to find it.”

To save North Atlantic right whales, vessels must move slower through whale habitat or avoid it altogether, and fishermen should use ropeless fishing traps, Moore said.

“As a veterinarian, I’ve long been concerned about how entanglements affect the welfare of these whales," Moore said. “Now we are starting to draw the linkages from welfare to this species’ decline.”

Caroline Enos can be reached at caroline.enos@globe.com. Follow her on Twitter @CarolineEnos.