I think it was Harper, and a boat load of Albertans. 

Probably all boozed up and speeding around in a rented oil tanker, just looking to grease Namu. I suspect that Harper, or one of the redneck Alberta boozehounds, were emitting orca calls, trying to draw the critters in, and then WHAM!

No doubt also throwing half empty beer cans overboard at all the freighter sailboats  bringing in valuable wares from Asia and sail-ferries transporting BC'ers and their bicycles between the mainland and Vancouver Island.

It is well known that these orcas live forever if undisturbed. There is no other explanation for this tragedy other than the one I have given, unless you want to speculate on crazy talk.

Anyways, it certainly is fortuitous, and not suspicious at all, that this holocaust was discovered just weeks after a series of articles describing how the KM pipeline and associated increases in tanker traffic would destroy these beautiful creatures, forever and ever and ever.