We need to be very careful here. There are those (not myself) who would contend that a fetus is a "person", thereby implying that abortion is "murder". I disagree with that, but if we say cetaceans are "persons" than is whaling then "murder"? Are we calling the Eskimo tribes who to this day hunt whales as part of their cultural tradition "murderers"? I am all for conservation, don't get me wrong, but willy-nilly throwing around the word "person" is not helpful, it is not helpful in the debate about reproductive choice and it is not helpful in the conservation debate either.
A more general idea that the more "conscious" (variously defined) an entity is, the more it should be treated humanely. That makes sense to me, and to most people I would think. But we need to figure out how to do this with getting into ethical quandaries like the ones outlined.
Yes, I call cannibalistic tribes murderers (provided any still exist, hopefully not). But my point is to not rush to make simplistic categories. My attitude on these and related issues is that it is enough work, more than enough work, for me to figure out how to live my own life ethically, without spending energies casting judgements upon others. Personally, I would never hunt dolphins or whales - I don't like hunting anyway and would not do that, heck, I take insects outside when I find them inside rather than stepping on them, lol - more seriously, yes, I find this research very compelling and for these reasons the concept of harming sentient beings is very troubling to me, and would not want to hunt a dolphin or a whale any more than, say, a visitor from another planet. That said, these are still complex issues which science can inform upon, but we need also to understand that in nature, in biology, one's own species is the priority, and so the "better angels of our nature" may and hopefully do go towards wanting humane treatment for more sentient creatures, but also let's not get on a bully pulpit on sensitive and complex matters. Again, I have found it is hard enough to try and be an ethical person for oneself, without trying to be judge and jury over others. That is my only point with the Eskimo tribe reference. :-)