The large number of dead whales appearing along the coast of British Columbia and Alaska since May is raising alarms among scientists.

Thirty dead whales have been detected in the Gulf of Alaska since May, representing a die-off more than three times the normal rate, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

Another six dead stranded whales have been reported along B.C.'s north coast over the same time period, also a significant increase above annual seasonal numbers.

Paul Cottrell, Pacific marine mammal co-ordinator with the Department of Fisheries and Oceans Canada, says his team is collaborating with U.S.officials to investigate the situation.

"We're working closely with NOAA to analyze samples," Cotrell said in a joint media teleconference, noting necropsy samples had been gathered from two dead humpbacks found in B.C. waters.

The prevailing theory is that a large toxic algae bloom off the West Coast might be to blame. However, scientists have been unable to make a concrete connection.

Only one sample, characterized as "less than ideal," has been analyzed to date. It came back negative for one strain of algae toxins.

Gathering good samples has proven challenging.

"Alaska has an awful lot of coastline and much of it is difficult to reach," said NOAA adviser Dr. Bree Witteveen. "We can't get to those carcasses more often than not."

As well, field scientists have encountered "predator competition" while trying to gather samples, as witnessed by the news release photo showing seven large bears feeding on a fin whale carcass near Kodiak, Alaska.

So far four whales species have been identified in what NOAA is characterizing as an "unusual mortality event": humpback, sperm, grey and fin.

The public is asked to report any dead whale sightings, but should not approach or touch the animal.

In B.C. people can call the 24 hour Marine Mammal Incident hotline at 1-800-465-4336.