A humpback whale that washed up dead on the shore of British Columbia's northern coast last week was the fourth to die in a week in the province's coastal waters.
The 10-metre-long female whale was found floating on its back near Klemtu, B.C., with several gaping cuts and a large gash above its tail that experts say indicate it might have been entangled in rope.
But while investigators from Fisheries and Oceans Canada are still trying to determine exactly how the large humpback ended up dead, the department says it also performed a necropsy – or animal autopsy – on a smaller humpback near Haida Gwaii on Tuesday, and at least two more were reported to be seen floating lifeless in the water within the last seven days.
"It's a concern and it's something that we're watching," said Paul Cottrell, a marine mammals co-ordinator with the Department of Fisheries and Ocean's Pacific Region who performed the necropsy on the Klemtu humpback. "We're hoping that if there is something out there that's common, we can find what that is."
The uptick in reported whale deaths comes as whale specialists say this summer has seen a record number of whale entanglements in fishing gear and nets.
Six of those entanglements were reported in the last month, Mr. Cottrell said, of which four were rescued.
And not far away, in southeast Alaska, there have been 21 deaths of fin whales and humpback whales in the past two months.
Among the largest whales in the world, humpbacks grow up to 16 metres in length and can weigh 40 tonnes. The species almost went extinct in the North Pacific in the 1960s after commercial harvesting decimated the population to a mere 1,500 whales. But in recent years, the whales have made a remarkable comeback to about 21,000 – 2,100 of which are using B.C. waters – and were even down-listed last year from "threatened" to "special concern" on Canada's list of species at risk.
"Each year we're probably adding to the population [in B.C.] between 80 to 100 more whales," said Andrew Trites, a whale expert with the University of British Columbia.
Mr. Trites said that since humpback whales are a species that use nearshore waters, there's a greater chance they will wash ashore and be seen by people when they die.
"We are seeing, literally, humpback whales recolonizing the entire coastline, which means that there will be more interactions both positive and negative with them," he said.
Others, like Max Bakken, a field technician for Pacific Wild, a non-profit group working to protect wildlife and their habitat, are alarmed at the spike in humpback deaths and feel a lack of fishing regulations that protect whales might be to blame.
"You can't police where the whales are going, but there could be some regulations [for fishermen]," he said. "There's nothing at the moment taking into account that humpbacks tend to get entangled in fishing gear."
He added that "people are kind of careless around whales, and there are very few safe zones for them. ... Just because their populations are rebounding, it's not the only explanation of all this stuff happening."
Mr. Bakken noted that higher shipping traffic in this area also poses a significant threat to the species, since humpbacks tend to sleep near the top of the water, making them very susceptible to ship strikes.
"These channels are sometimes so clogged with whales laying about the surface that you couldn't actually safely navigate a B.C. ferry through them," he said. "Most of the time, whales get out of the way, but the more shipping we have up in this area, the higher the chances are."