You picked two very interesting species there.

Generally speaking, animals don't take {-pu'}.

But we have seen on screen evidence that whales are capable of communicating with extraterrestrial species. 

And dolphins serve as crew on the Enterprise-D.

That said, just because my cats are able to communicate various things to me, doesn't mean that the qualify for {-pu'}.

So I'd leave whales at {-mey}, but I'd use {-pu'} for the dolphins in Cetacean Ops if for no other reason than to show respect as they are a part of the crew.

But I'd leave everyday dolphins at {-mey} unless I was talking about them in a specific instance where they were trying to thank me for all the fish.

~naHQun