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Dr. Pierre-Yves Dumont collects samples from a dead right whale in the Gulf of St. Lawrence in a recent handout photo.The Canadian Press

Federal fisheries experts are looking for a shore where they can dissect massive North Atlantic right whales to determine whether it was a ship strike, an algal bloom, or some other menace that killed at least six of the endangered creatures in the Gulf of St. Lawrence over the past month.

The mysterious deaths of the right whales, which were once abundant in the Atlantic Ocean but have been reduced by overfishing to just more than 500 animals, means that more than 1 per cent of the species was wiped out in June alone. And scientists, so far, do not understand why.

The carcases are now floating near the Magdalen Islands, northeast of Prince Edward Island. Fisheries experts managed over the weekend to take a few samples of blubber and muscle, and three of the whales have been tagged so their bodies can be tracked.

But the tests at sea have, so far, been insufficient to pinpoint what caused such a catastrophic die-off. So the Department of Fisheries and Oceans (DFO) is looking for somewhere on land that can be reached by heavy equipment, but that is not near local populations or tourist sites, to which the beasts can be dragged and where necroscopies can be performed to provide a definitive answer.

"This is an unprecedented event and such a huge, huge loss for the North Atlantic right whale population," said Sigrid Kuehnemund, the lead ocean specialist with the World Wildlife Fund-Canada.

"The loss of one whale has a huge impact for any endangered species, but in particular for the North Atlantic right whale," Ms. Kuehnemund said. "Looking at this number of deaths, it will take such a devastating toll on the population. And we know that, of the whales that have been sighted, at least two are females. So, we're not just losing those whales but also the potential for those females to have calves into the future."

The first dead whale was found by the Coast Guard in the gulf on June 6. It wasn't until June 18 that there was another sighting. Since then, they have been turning up in numbers that have caused scientists significant concern.

At the moment, it is unclear just how many whales were killed. DFO officials have confirmed at least six different carcases but there have been reports of others.

Isabelle Elliott, a senior fisheries and aquaculture adviser with the DFO, told reporters on Monday that she and her colleagues are analyzing the data of air and sea surveillance to rule out whether the same whales have been spotted twice.

Ship strikes are the most common cause of death for right whales, said Ms. Kuehnemund. They are slow and curious creatures, she said, and, when they hear a sound that interests them, they tend to hover about five metres just below the surface of the water where they are not spotted by navigators until it is too late.

The whales that have been found floating this month in the Gulf of St. Lawrence do not show any direct sign of injury. But it is only when the scientists can dissect them to see if bones have been broken or skulls crushed that ship strike can be ruled out, Ms. Elliott said.

In this case, Ms. Kuehnemund said, with so many of the animals being killed at about the same time, the investigators will have to look at other possibilities including algal blooms.

Although pods of North Atlantic right whales have never been known to be killed by toxic algae, it has happened to humpback whales in the United States. And Ms. Kuehnemund said there is at least one case in which a bloom killed southern right whales off the coast of Argentina.

Sabine Jessen, the national director of the ocean program of the Canadian Parks And Wilderness Society, said her group is disappointed that Canada decided to declare only certain parts of the Bay of Fundy to be critical habitat for the endangered North Atlantic right whales. The United States has taken steps to protect them throughout their entire range, she said.

Ms. Kuehnemund said the World Wildlife Fund is urging for the government of Canada to develop a network of marine protected areas to shelter the whales from the impact of human activities including ocean noise, ship strikes, and entanglement in fishing gear. "But unfortunately," she said, "there are other threats to these creatures in addition to human threats and sometimes they can be natural."

The Vancouver Aquarium and the National Oceanic and Atmospheric Administration are gathering samples from the exhalation from humpback whales using a drone