The carcass of a seventh North Atlantic right whale has been found off the Magdalen Islands in the Gulf of St. Lawrence, reports Radio-Canada.

The Canadian Coast Guard discovered the dead whale near Havre-Aubert on Wednesday night.

Quebec's marine mammal research network, known by its French initials GREMM, confirmed to CBC's French-language service that it was not previously aware of the carcass.

Tonya Wimmer, with the Marine Animal Response Society, said the whale is a male, and it was badly decomposed. She also said it isn't clear yet what caused the whale's death, The Canadian Press reported.

The Department of Fisheries and Oceans told CBC News in an email that it is investigating the whale carcass to determine if it is a new one or a carcass that has been previously identified.

Six other North Atlantic right whales, which are an endangered species, have been found dead in the Gulf of St. Lawrence since June.

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Researchers from the Marine Animal Response Society examining one of the dead right whales. (Marine Animal Response Society)

Necropsies conducted on three of them found two suffered blunt impact injuries, likely from collisions with ships, and the other had a "chronic entanglement."

Scientists involved in the necropsies said other causes may be possible but could not be confirmed because of the advanced state of decomposition.

Factors such as parasites and biotoxins produced by algae bloom have also been put forward as possible causes of death.

Another of the first six dead whales has now reached the shore of Corfu Island in the Magdalen Islands and a further necropsy may be conducted.

With only 525 whales left in the species, the "unprecedented die-off" represents more than one per cent of the population, the Marine Animal Response Society said in response to the earlier deaths.

The organization says ships are dangerous to whales and either need to be rerouted away from the whales' feeding grounds or forced to slow down.

With files from Radio-Canada's Caroline Cyr