The article goes on to mention that Duane wrote Hwiii into Dark Mirror as a present to Rick Sternbach, who had apparently written cetacean crew into the TNG bible only to have them out.
The dolphins aboard ship were mentioned in passing in "The Perfect Mate," and referred to in The ST:TNG Technical Manual
as navigational specialists.
Geordi's address to the Ferengi, right? "Listen... have you been down to see the dolphins yet? You really shouldn't miss them..."
We needed more cetaceans.