A right whale found dead in Canada's Gulf of St. Lawrence is likely to have died in a collision with a ship, officials say -- a worrying conclusion as experts fear for the future of the critically endangered species.

Preliminary findings from a necropsy on Comet, one of six dead whales found since the start of June, are "highly compatible with death due to blunt trauma, consistent with vessel strike," Fisheries and Oceans Canada said.

Final results of the necropsy will be available "in the coming months," the government department said in a statement late Saturday.

The same conclusion was drawn about the death of Punctuation, a 40-year-old female right whale. Analysis of the remains of male whale Wolverine were inconclusive.

An autopsy on Clipper is set for Monday, and options are being considered to perform similar tests on the remaining two whale carcasses.

This month's right whale deaths, as well as seven recent calf births, bring the total population estimate to 412, Canadian officials say.

Transport Canada has expanded the area of the Gulf of St. Lawrence under a shipping speed limit of 10 knots and closed 16,000 square kilometers (6,200 square miles) to commercial fishing in a bid to protect the whales.

These are the first right whale deaths reported since 2017.

Conservation officials say that North Atlantic right whales are among the most threatened species in the world.

About a third of them visit Canadian waters to feed each summer, with the number of visits increasing and the whales' range in the Gulf expanding in recent years amid changing oceans.