Humpback whales are returning to B.C. waters in the largest numbers seen in decades.

But some researchers believe the province's coast is becoming perilous for those returning humpbacks because of debris.

Back in mid-September, Fisheries and Oceans Canada (DFO) was able to free a whale from a line and anchor; but last week, another humpback whale died after getting tangled in fish farm equipment.

"They behave very, very differently from toothed whales like orcas," researcher Jackie Hildering with the Marine Education and Research Society told All Points West host Robyn Burns.

"They don't have biosonar like toothed whales do, so they can be terribly oblivious to boats … and therefore also, of course, where gear is, especially if they're lunge-feeding."

Preliminary research by the Marine Education and Research Society and DFO suggests 47 per cent of the more than 2,000 humpbacks seen along the B.C. coast have scarring that indicates they have become entangled and survived.

They say it's not possible to know how many have died because most whale carcasses fall to the sea floor or wash up on the coastline badly decomposed.

Hildering says it's time for stronger regulations and better knowledge about how gear from fish farms and boats can cause these incidents.

Dead humpback whale near Klemtu B.C.

In August, a humpback whale washed up near Klemtu, B.C. A wildlife guide who found it says it likely died because it was entangled by rope. (Philip Charles/Facebook)

She says anyone who sees an entangled whale should report the location to the DFO Incident Line at 1-800-465-4336 or via radio at VHF channel 16.

She advises people to remain with the whale, at a distance, until help arrives and not to attempt to untangle the whale without professional assistance.

With files from CBC Radio One's All Points West

To hear the full story, click the audio labelled: Researchers fear B.C. coast becoming dangerous for returning whales