A Canadian surveillance plane was scouring the waters of the Gulf of St. Lawrence when it made a grisly discovery: the carcass of a North Atlantic right whale, one of about 400 remaining in the world, was drifting in the current out.

From there, the news would only get worse. The next day, another dead whale was spotted in the same body of water, and an 18-year-old right whale was entangled in a fishing gear near Quebec, with a rope cutting through its head and over its vent.

It's been a devastating summer for the endangered marine mammal. Since early June, eight North Atlantic right whales - or 2 per cent of the world's population - have been found dead in Canadian waters, alerting scientists, conservationists and government officials who believed they had begun to make progress in protecting the endangered species.

"It's a terrible step toward extinction," said Regina Asmutis-Silvia, executive director of Whale and Dolphin Conservation USA. "They're a discrete superhero and we're losing them."

Necropsy results are still pending for most of the whales, but preliminary findings for three of them suggest naval strikes.

Of particular concern with this year's deaths is that four of the whales that were killed were females, of which fewer than 100 remain. Reproduction rates have dropped 40 percent since 2010, according to scientists at the Woods Hole Oceanographic Institution, making the deaths of the females a major blow.

"Currently, this is clearly not sustainable," said Philip Hamilton, a researcher at the New England Aquarium in Boston. "At this rate, in 20 years, we won't have any breeding females left and the population will be effectively extinct."

North Atlantic right whales are already on the brink of extinction. Whalers considered the docile, slow-moving creatures full of oily blubber the "right" whales to hunt, and a century ago, they slaughtered nearly all of them. Those practices changed in 1935, when the League of Nations made them illegal. Throughout the 20th century, their numbers slowly rose, though they never recovered.

Then, in 2010, the population began to decline again - and scientists have been racing against the clock to find out why.

Many say the decline is linked to a change in the whales' migratory pattern, possibly as a result of warming waters. They are showing up in unforeseen areas where there are few regulatory protections for them.

This made them susceptible to fatal blows from fast-moving ships or entanglement in fishing lines, which can cut flesh and bone, slowly and painfully killing the whales by drowning, starvation or infection.

Researchers have found that 88 percent of fin whale deaths for which a cause was determined in the past 15 years were the result of vessel attacks or entanglement. None of the deaths, they reported in a study published last month in the journal Diseases of Aquatic Organisms, were the result of natural causes.

Traditionally, whales have spent the winter in Florida and Georgia, moved north to Cape Cod Bay in the spring and to the Gulf of Maine and the Bay of Fundy for the summer. But in recent years, they've been showing up farther north in the Gulf of St. Lawrence.

Scientists blame climate change. As the whales' usual habitats have warmed, they theorize that the copepods they like to eat have moved north. The whales have followed them.

"Whales are showing up in areas we haven't seen them before," said Jonathan Wilkinson, Canada's fisheries minister. "It's harder [to address the issue] when the whales are moving."

For conservationists, this year has been a bad case of déjà vu.

Seventeen North Atlantic right whales died in North America in 2017, including 12 in Canada, in what the National Oceanic and Atmospheric Administration said was an "unusual mortality event." The deaths were human-caused - the result of entanglement or vessel strikes.

"That was kind of a light moment for a lot of people about how serious this issue was," said Tonya Wimmer, executive director of the Marine Animal Response Society in Nova Scotia.

The Canadian government has implemented measures that include speed limits for certain vessels, a temporary ban on lobster and crab fishing in certain parts of the Gulf of St. Lawrence and increased aerial surveillance of the waters.

The restrictions were tightened in 2018 - and they seemed to be working. Last year, no right whales were found dead in Canada. So officials relaxed, to minimize the impact on the industry.

But after the first of the deaths this year, the Canadian government has tightened the rules again. The area in which speed limits apply has been expanded, as have the categories of boats that are subject to it. Aerial surveillance has been increased and enforcement for fishing closures are stricter now.

Hamilton says reducing rope strength on fishing gear and expanding areas subject to speed limits can reduce fatalities. New technologies, such as rope-less fishing gear, also hold promise.

Fisheries Minister Wilkinson told reporters in New Brunswick this week that he is open to the idea of tipless fishing gear, but noted that it comes with a "cost issue" and an "adjustment issue" for fishermen.

Wilkinson says it's not easy to find a balance between protecting whales and reducing the impact on the industry. He said the welfare of the species is "the first and foremost thing we have to focus on."

Wimmer applauds the government's actions, but says she doesn't think she's found the right balance between animal welfare and protecting the industry yet.

She was present at the necropsy of a 40-year-old whale that was known injuries known as punctuation - because of the small scars on its head that looked like commas and dashes.

The whale, found dead in the Gulf of St. Lawrence in June, was struck so hard by a vessel that its organs began to protrude from a six-foot gash in its back.

Wimmer says she also has scars from scoring injuries.

"It's an absolutely horrible thing to see."

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