See my comment below, but orcas do not switch up their food source very readily unless they are in an ecotype similar to the transients found in the Pacific Northwest. Orcas that specialize in fish do not switch up, even in the face of dire straits, even though they could. This is at least so far. Orcas' splitting up into ecotypes is almost solely cultural and not biological, and so even though we wish orcas wouldn't have to struggle, I feel we could potentially see them adapt to other food sources, but that so far has not been observed.

The orcas that eat mammals have more varied diets and thus hunting techniques, since their food source requires that (mammals are smart, have good eyesight and hearing, etc.).