I agree. Orca is a confusing animal and all the people are not aware of orca's. So I guess it's better to go for shark's.
And in addition I think that the sequence should be like this plankton, minnows, dolphins,shark's and whales if you classify them on the basis of size. But I see that in your sequence the dolphins are placed after shark's, that is if you classify them on the basis of intelligence, the dolphins are the most intelligent mammals on the earth. So in my opinion the classification should be on the basis of size. And the categories must be made on steem power.