Another North Atlantic right whale has been found dead, this time off Martha's Vineyard, the Massachusetts island south of Cape Cod.

Ten right whales have died in the Gulf of St. Lawrence since June 7 — four of them washing up on the west coast of Newfoundland in the past week alone.

In addition to the 10 whale deaths in the Gulf, the Cape Cod Times reported that a right whale died in Cape Cod Bay in April.

The latest dead whale was discovered Tuesday, floating offshore near Edgartown, M.A., said Jennifer Goebel, a spokesperson for the National Oceanic and Atmospheric Administration.

A necropsy on the whale began Wednesday, but the cause of death may not be known for two months. (International Fund for Animal Welfare)

Goebel said that on average, the agency finds about three of the endangered animals dead every year.

"We confirmed that this was a North Atlantic right whale with advanced decomposition," said Goebel.

She said the degree of decomposition indicated the whale had been dead for some time.

A necropsy started Wednesday, but Goebel said it will likely take months to find the cause of death.

Collisions with ships and entanglement in fishing gear are suspected in the earlier whale deaths.

"As far as we know, they're all part of the one North Atlantic right whale population," Goebel said.

The whale had been dead for a while, says a spokesperson with the National Oceanic and Atmospheric Administration. (International Fund for Animal Welfare)

Fewer than 500 North Atlantic right whales remain.

'Unprecedented' whale deaths

In June, six right whales were discovered floating dead in the Gulf of St. Lawrence. Necropsies were performed on three of them.

Two died as a result of trauma, which suggested collisions with ships, and the third died of entanglement with fishing gear.

By the middle of July, eight right whales had died, with the number rising higher as whales were found off the coast of Newfoundland.

It's a critically endangered population, so these deaths are certainly catastrophic. - Jennifer Goebel, NOAA

"It is a catastrophe, to say the least," said Sigrid Kuehnemund, lead specialist in oceans for the World Wildlife Fund.

"Nine deaths represent one to two per cent of that population. It's a critically endangered population, so these deaths are certainly catastrophic."

Goebel said right whales can be hard to spot from a ship because they do not breach the way humpbacks do.

Dominic LeBlanc, the federal minister of fisheries and oceans, previously said his department is working on preventing more deaths.

The government is prepared to "take all necessary steps," he said.

The department had no comment about the whale found dead off Martha's Vineyard, since the area is outside Canadian jurisdiction.