A badly decomposed carcass that washed up in Massachusetts is being counted as the 17th North Atlantic right whale to die during a brutal year for the endangered species.

On Nov. 27, the remains of a right whale were found on a beach on Nantucket, an island off Cape Cod.

Researchers were initially hesitant to add the animal to this season's tally of dead right whales out of concern it had already been counted floating at sea in August.  

They have since decided this whale will be considered "Whale 17."  

"And trust me, no one would be more thrilled if we in fact confirm that this is not a 17th carcass, that it is the same as the one that was seen in August," said Heather Pettis, an associate scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium in Boston.

"I would love to be wrong."

Nantucket whale carcass

Blubber and bone are all that is left of a North Atlantic right whale found on a Nantucket beach late last month. (International Fund for Animal Welfare)

Genetic testing will be used to determine with certainty if the classification is correct, but results could take months.

The carcass found on Nantucket was what scientists call deflated, because a whale's internal organs decompose at a much faster rate than its blubber exterior.

The mass of organic matter was identified as a North Atlantic right whale by its distinctive flippers, which decompose at a slower rate than the rest of the carcass, said Marianna Hagbloom, a research  assistant with the Anderson Cabot Center.

"We try to be as conservative as possible when saying that a new carcass has been identified," Hagbloom said. "And so, we are announcing this assumption that we're making, but we wouldn't have done that lightly."

Cause of death unknown

Four per cent of the North Atlantic right whale population died this year, a massive loss for a species that numbers fewer than 450.

The researchers said they may never know how the 17th whale died, but some of the others found this year were hit by ships or got entangled in fishing line.

How an unprecedented number of deaths put the endangered North Atlantic right whale's future in peril2:57

Several factors were taken into account before adding the whale to the list of dead, including identifying physical features that were not seen on the whale carcass spotted in August.

"There were some indentations that suggest scarring of some sort," Pettis said. "Scars are one thing of many that we use to identify individuals."

Awaiting genetic testing

An ocean drift analysis was also done on the dead whale discovered at sea to project where the carcass would eventually wash up. While it is possible that whale could have drifted to Nantucket, the analysis suggested otherwise, Pettis said.

"There is some evidence to suggest that this is a new whale," said Pettis, who is also the executive administrator with the North Atlantic right whale consortium. "But we can't confirm that until we have the genetics." 

CBC New Brunswick produced a six-episode podcast on the deadly summer for North Atlantic Right Whales. You can find it at cbc.ca/podcasts, or search for "Deep Trouble" on iTunes.