As many as five killer whales that usually swim with pods along the B.C. coast have been missing for more than a month and researchers say they fear the marine mammals may be dead.

Three of the orcas belong to the southern resident population, which is found off southern Vancouver Island, Haro Strait and the Strait of Juan de Fuca.

There are concerns that B.C.'s killer whales could be starving, or are being poisoned by PCBs.
(CBC)

That population of just 87 whales is already endangered and two of the missing orcas are breeding females, with one nursing a calf, Department of Fisheries and Oceans scientist John Ford said Friday.

"Losing young animals like this from the population is not a good thing because for the population to grow, it really needs as many productive females as possible."

Ford, who has studied B.C. killer whales since the 1970s, said he's not sure what's wrong, but says the whales may be starving from a lack of salmon or poisoned by toxic PCBs that accumulate in their bodies.

Another possibility is that industrial noise could be disrupting their internal navigation systems, he said.

"It's really rare for us to be able to find an actual cause of death. That's why we're trying to just give it our best judgment about what the threats are, what the pressures are facing the whales. "

Ford points to the fact the southern resident population had been slowly growing after a steep decline in the 1990s, and said he worried the recent disappearances might signal another alarming turn.