Are dolphins a sentinent species?
Should they been given protection?
Of course. But that has nothing to do with them being sentinent.
Should they be treated different to other protected species, possibly even given the same status as humans?
Probably when they start knitting pullovers.
How about the other whales?
Orcas and other whales are extremely intelligent. But then again, Orcas are huge, sadistic assholes as well.