Sarge,
I did some research into what you are saying about the orcas killing the sea otters, and there may be some credence to that. However, I think it is a case of many causes contributing to their decline, and one of those causes is oil, another, lack of a suitable diet, which affects the reproductive capabilities of marine animals.

In the 1700's the sea otter population was estimated to be about 300,000 but by the early 1900's the sea otter population was estimated to be as low as 2000, because of the maritime fur trades. (Directly attributable to humans).

Oil is very detrimental to sea otters. When oil get on a sea otters fur, its weight forces out the air from between the sea otters hairs, which is the only insulation sea otters have from the ocean. Unlike sea lions and seals, otters have no insulative blubber layer. The air between their hairs keeps them dry as well as insulating them. So, when a sea otter gets covered in oil, it is instantly exposed to freezing water temperatures. The exposure causes hypothermia and death.

We wouldn't even be talking about whether or not we were responsible for the recent decline if we hadn't nearly caused their extinction during the fur trade years. So, yeah, we are responsible, killer whales or not.

Some of us do believe that humans and their dominion over the planet are a part of the evolution of the world and the consequences we have to bear are a part of that. I believe that as humans we are being given a chance to do something that no species has ever done before. Prevent its own extinction.