At a recent meeting of the American Association for the Advancement of Science, researchers agreed that dolphin and whale brains actually have a complexity that rivals human brains, and that they also possess a sense of self. As such, the deliberate killing of these individuals is as ethically wrong as killing a human. You can read more about the conference in animal cognition expert Marc Bekoff's commentary in Psychology Today.
On a somewhat related note, the AVMA says that the human-animal bond will be emphasized at its 2013 convention. You can read more about that conference in JAVMA News. (Speaking from personal experience, no matter what vets say at their conferences, I'll wait for the AVMA to put its money where its mouth is... and stop defending (and trivializing) all vet mal suits on the grounds that animals have no market value and therefore - even if the vet did something wrong - they don't owe much or anything to the family of harmed animal.)