Researchers are scrambling to figure out why one of the world’s most endangered whale species is dying in “unprecedented” numbers, after at least 10 north Atlantic right whales have been found floating lifelessly off the coast of Canada.

The first whale carcass was reported in early June. Within a month, another six reports came in, leaving researchers reeling. This week, after several carcasses washed up on the shores of western Newfoundland, Canadian officials confirmed that the number of whale deaths had risen to at least 10, making 2017 the deadliest year for the whales since researchers began tracking them in the 1980s.

“This is a huge blow to the recovery of the north Atlantic right whale,” said Moira Brown of the Canadian Whale Institute. “This is an animal that maybe numbers 500 animals.”

The north Atlantic right whale – which lives along the eastern seaboard of Canada and the US and can reach up to 16m (50ft) in length – has struggled since being nearly hunted to extinction by whalers in the late 18th century.

Brown described the string of deaths as unprecedented. “We’re now looking at having lost about 2.5% of the known population. And it’s at least double – if not slightly more – than the number of calves born this year.”

Scientists are frantically carrying out tests on two other, rapidly decomposing whale carcasses to determine whether they are among the whale deaths that have been previously counted. If not, the tally could rise in the coming days.

With no obvious causes for the deaths, a team including federal scientists, pathologists and veterinarians have been racing against time to figure out what is happening. Necropsies have been carried out on several of the whales – using a backhoe to enter the large animals – in hopes of finding clues before the carcasses decompose.

The preliminary findings suggest some of the whales might have collided with vessels. “We have three animals with evidence of blunt trauma and one was entangled in snow crab gear, so we know there are some human activities that are involved,” said Brown.

In recent years, researchers have noticed the whales moving into the Gulf of St Lawrence in large numbers – possibly lured by the greater availability of food – leading to increased interactions with humans.

The initial findings still don’t explain why the deaths have seemingly occurred within such a short time frame. As scientists move into the laboratory to carry out further analyses, some have speculated that the deaths may have been caused by toxic algae or something the whales ate.

In the meantime, Canadian officials said they were taking steps to protect the dwindling population. A snow crab fishing area in the Gulf of St Lawrence has been closed while mariners have been asked to voluntarily reduce their speed to 10 knots or less in certain areas, the department of fisheries said in a news release.

The full results of the necropsies – which could take months to obtain – will likely offer insight into long term solutions to halt what has become a catastrophe for the species, said Brown. “We need to have patience at this point in time and it’s a very difficult thing to have. But we need to wait for the full story.”